65
The underground railroad 
post office in 
Postumia Grotte 1872?19451
Thomas Lera
The first cavern to achieve worldwide renown as a showplace was Adelsberg Cave, located 
near a village of the same name in Austria. From 1872?1945, it had three other names: Adels-
berger Grotte, Postumia Grotte and Postojnska Jama (Figure 1).
Exploration began as early as the thirteenth century, but the cave received only modest 
attentions until 1818, when a decision was made to commercialize the cave. Workers cleared 
away rubble and climbed rickety ladders to install torches for light. In the process, one laborer 
happened upon a gap in the cave?s far wall, some ninty feet above the floor. Crawling through 
the opening, he found a new section far larger than the first with fantastic dripstone formations.
Local officials reasoned, if the problems of access could be conquered, the public would 
find it irresistible. Workers continued to level paths through the chambers, built a wooden 
bridge across the cave?s underground Pivka River, and chiseled stone stairways into the walls 
made safer by wooden handrails. The crude torches were eventually replaced with chandeliers 
and oil lamps, and guides were trained. 
When the railway linking Ljubljana and Trieste via Postojna was opened in 1857, access 
became easier and interest in the cave even greater. On March 11, 1857, Emperor Franz Joseph 
and Empress Elisabeth stopped in Adelsberg to visit the cave on their way home from Italy. 
Adelsberg Cave was soon drawing 1,000 visitors a year, and by the 1870s the annual num-
ber of tourists had soared to 8,000. After visiting Adelsberg in 1881, a reporter from the New 
York Times (1881) wrote in awe of the ?stalactites of unequaled splendor,? and the ?fantastic 
architecture in the cave,? and concluded ?though it possessed neither the mighty expanse of 
the Mammoth Cave of Kentucky, nor the delicate beauty of the Blue Grotto at Capri, every 
part of it is filled with a stern and gloomy grandeur which is indescribably impressive.?
To avoid confusion, and keeping in line with naming conventions, all references in this 
article to locations in the cave will be in Italian (also found on the map below). However, 
most places have alternative names in both Austrian and Slovenian.
1. Between 1872?1945, the cave had three names Adelsberger Grotte / Postumia Grotte / Postojnska 
Jama because different countries (Austria, Italy and Yugoslavia) occupied the surrounding territory.
66 Thomas Lera
The trains
The problem of making visits more comfortable, safer, easier, and more comfortable was 
resolved in 1872, when the Cave Board decided to install rail tracks into the cave 1.4 miles to 
Calvario (Figure 2). Since the path through the cave did not have many changes in elevation, 
the Board decided that the carriages in the cave could be driven by manpower. 
Figure 1. Postojna, Slovenia, is located about twenty-five miles from Trieste, Italy.
Figure 2. Map of Postumia Grotte showing Railway (Ferrovia?dashed line) and Walkway 
(Strada?red solid line).
The underground railroad post office in Postumia Grotte 1872?1945 67
The first underground commercial railway in the world began operation on June 16, 1872. 
The part of the cave it originally took visitors half an hour to explore could now be seen in 
five minutes from the elegant double-seated carriages called ?Faetons? (Figure 3) (Slovenski 
1872). Visitors could use the carriages in one or both directions, into and out of the cave. The 
round-trip ticket cost 1 florin, a one way ticket 70 kreutzers. In 1920, entrance into the cave 
was 15 lira and a roundtrip train ticket was an additional 5 lira (Figure 4).2
By 1914, the small, manually operated railway became outdated due to the large number 
of visitors, and the cave humidity had decayed many of the railroad ties. The Cave Board con-
tacted the Orenstein & Koppel factory and ordered a locomotive and carriages, of the type usu-
ally used in mines (Borjan?i? 1992). The locomotive, named ?Montania,? had a one-cylinder 
water-cooled 6?8 Brake Horse Power (BHP) petrol engine with two axles (Il Popolo 1924).
Figure 3. The Faeton, photograph by M. ?eber, Postojna.
2. For comparison costs at that time $1 US was equal to 19 lira.
Figure 4. Tickets from the 1920s to enter the cave and ride the train. 
68 Thomas Lera
Plans to improve the railway were interrupted by the outbreak of the First World War. 
Then in the early 1920s, the Italians, who now controlled the area, continued improvements, 
including completing the railway, upgrading the electrical system, removing the monuments 
praising Austrian emperors, and employing foreign language speaking guides.
The Italian patriotic feelings were strong after World War I. Italians believed ?the Austrian 
and Slovenian names of dripstones and formations were infantile? and replaced them with 
the names from Roman mythology, for example Franz Joseph und Elisabeth Grotte became 
Braccio Mediano (Shaw 2006). (Around 1945, Yugoslavia changed it to Male jame.)
The improved underground railway system from the cave entrance to Calvario was com-
pleted in 1923. Between April and June 1924 the first test-drives were performed with the 
locomotive ?Montania No. 803.? On August 2, 1924, the new underground railway was of-
ficially opened (?uk 2003). The locomotive hauled five four-seat carriages into the cave four 
times a day (10 a.m., noon, 2 p.m. and 4 p.m.).
Based on the growing popularity of the cave, the Cave Board decided to purchase additional 
locomotives and carriages. On March 27, 1925, Orenstein & Koppel sent from their factory in 
Nordhausen, a new ?Montania, S-10, No. 2044? with a more powerful petrol-driven, three-
axle locomotive and new carriages with six adjustable seats (Figure 5). A year later, in July 
1926, the Cave Board bought a third 20 BHP petrol-driven locomotive ?Cemsa, Type 20 G, 
No. 20-779,? manufactured in Milan. There were now three trains with thirty-one carriages 
which took tourists into the cave eight times each day (?uk 2003, 235).
A journalist from the Bologna newspaper Il Resto del Carlino3 (1925) visited the grotto 
and wrote: ?It is 4 p.m. The train stops on the platform in front of the cave, having passed the 
75-metre long gallery, acting as the underground railway station. We boarded the train and 
the guide rang the bell to announce the departure of the train. Those who decided to visit 
the cave on foot, follow the guides. There are some elderly people and quite a lot of ladies 
and children on the train. The train slowly reaches Calvario, the final railway station with 
the turning point for the locomotives. There the train waited for the visitors who explored 
Figure 5. Montania S-10, Ufficio Postale R.R. Grotte (Official Postcard of the Royal Caves).
3. Carlino is one of the oldest newspapers and symbol of the city of Bologna since March 21, 1885, 
when it was first published.
The underground railroad post office in Postumia Grotte 1872?1945 69
further and took them back to the cave entrance along the same route. On its way back the 
train stopped near La Sala da Ballo, by the old post office where the visitors posted their 
postcards during a ten-minute break? 
In 1928, there were significant changes to the entrance of the cave with the construction 
of the Cave Board Administration Building, the entrance platform with the railway station, 
and the reception area (Figure 6). Now located between the headquarters and rock cliff was 
a new, visitor-friendly railway station with two tracks and a raised platform offering a safer 
and more comfortable access into the cave. This entrance was used for visitors wanting to 
see the cave from the train, while those who wanted to visit it on foot continued to enter 
through the main entrance.4
The post offices
In 1899, the Austrian Ministry of Commerce agreed to the Cave Board?s proposal to build 
and operate a post office inside the cave. The post office (Figure 7), built of stone, was about 
13 feet long by 6.5 feet wide, with a low-pitched roof. There was a door at the north end, two 
window openings for sales counters and a slot for mail. It was built about 1,650 feet from the 
cave entrance (Figure 2). 
Its customers were regular tourists and those attending the special twice-yearly festivals 
called Grottenfests held in the La Sala da Ballo with the dance hall specially illuminated. In 
1910, Juvanec5 reported that there were tables and seats outside the building for visitors to 
write their postcards.
For the Whit Monday (Pentecost) Grottenfest, the postal authorities authorized a special 
?Adelsberger Grotte / Postojnska jama? cancellation as seen in Figure 8. The postal authorities 
allowed the special postmarks to be used throughout the season from March first to November 
first, starting as early as 1899 (Adelsberg 1912). The other Grottenfest was held at different 
times in the autumn months.
Figure 6. Station platform in 1929 with the CESMA locomotive and carriages. Ufficio Postale 
R.R. Grotte (Official Postcard of the Royal Caves)
4. The visitors could choose between visiting the cave by underground train or on foot until 1963. After 
that year all visitors were required to use the underground train.
5. His photographs of the cave and its surroundings were used as illustrations on many postcards of 
the day.
70 Thomas Lera
There was a special cancel, a forerunner of a slogan cancel, for the 1912 Grottenfest when 
the Liedertafel Choral Society from W?hringen performed in the cave (Figure 9). 
There were several handstamps which had been applied in the cave on postcards. It is not 
known if the Austrian postal clerks applied these handstamps or if the handstamp and ink 
pad had been available at the counter for visitor use (Figure 10).
At Christmas 1915, two special military field post office postmarks were used?K. u. k. 
Grottenfeldpost 81. Kriegsweihnachten 1915 (Imperial and Royal Cave Mail 81. War Christ-
mas 1915) and K. u. k. Grottenfeldpostamt 81. Kriegsweihnachten 1915 (Imperial and Royal 
Cave Field Post Office 81. War Christmas 1915) (Figure 11). All military field post offices 
Figure 7. The Austrian post office in 1900 as seen on a multiple language post card, photo-
graph by M. ?eber, Postojna.
Figure 8. Postcard mailed on Whit Monday, May 20, 1907.
The underground railroad post office in Postumia Grotte 1872?1945 71
were numbered and, although their locations were not fixed, number 81 was at Postojna in 
1915 and 1916 (Rainer 1995).
This post office building remained in use until 1927 (with the Italian ?Postumia (Grotte)? 
postmark used after 1922), when it was replaced by a new building located 1.4 miles inside 
the cave (Shaw and ?uk 2003).
The Austrian / Italian post office
At the end of World War I, on September 10, 1919, the Treaty of Saint-Germain-en-Laye 
was signed recognizing the independence of Hungary, Czechoslovakia, Poland, and the State 
of Slovenes, Croats and Serbs. Parts of Austria were incorporated into the newly created states 
of Czechoslovakia, Poland, and Yugoslavia (the ?successor states?) and Trentino, South Tyrol, 
Trieste, Istria and several Dalmatian islands were ceded to Kingdom of Italy. Then in 1920, 
the Treaty of Rapallo, be-
tween the Kingdom of 
Italy and the State of Slo-
venes, Croats and Serbs 
(renamed Yugoslavia in 
1929), was signed to re-
solve additional territorial 
disputes. According to this 
treaty, the western part of 
Figure 9. Grottenfest in ADELSBERG W?hringer 
Liedertafel [Choral Society] (Van der Pas 2010). 
(Courtesy of The Speleo Stamp Collector).
Figure 10. Unique handstamps.
Figure 11. Austrian army 
field post office postmarks 
for the cave at Christmas 
1915.
72 Thomas Lera
the former Duchy of Carniola territory, including the town of Postojna, was ceded to Italy. 
Adelsberg Cave now came under Italian control and was renamed Postumia Grotte. 
The post office seems to have been resurrected between then and September 17, 1922, 
the official reopening of the cave at the traditional autumn festival (Il Resto 1922). The cave 
continued to operate on a regular, non-festive basis. 
While a 1924 guidebook indicated the old post office 
was open only during the traditional cave festivals, post-
cards put in the letter box on any day were dispatched 
with the special Postumia (Grotte) postmark. Because of 
the ten-minute train stop at the post office, many tables 
were occupied by hundreds of people daily who were in 
a hurry to write postcards purchased at the nearby post 
office counter (Perko and Gradenigo 1924). The post of-
fice was refurbished in the first half of 1924, and soon after 
roofs were erected over the visitor tables to shelter them 
from the dripping cave ceiling occurring after long periods 
of rain. By this time there were four clerks working in the 
post office (Figure 12) (Urbani 1925).
The ?POSTUMIA (GROTTE) ?? cancellation used, 
between 1923 and 1926, was 28 mm in diameter. Another 
cancellation of the same size, ?POSTUMIA GROTTE ? 
TRIESTE ?? (Figure 13), was used only in 1927. 
Exactly when the Austrian post office ceased to be used 
during Italian occupation is not known. However early in 
1927, a large, newly built post office was opened in Concert 
Hall in the Calvario, and both post offices operated together 
Figure 12. The Austrian post office with rubble cleaned up showing a letter box between 
the two windows. The Italian Postal Administration reprinted the Austrian postcard and 
added ?L?Ufficio della R.R.Poste Nelle Grotte (The Official Post Office of the Royal Cave).? 
Ufficio Postale R.R. Grotte (Official Postcard of the Royal Caves). 
Figure 13. Examples of the 
grotto cancels. 
The underground railroad post office in Postumia Grotte 1872?1945 73
for a period of time. Newspapers of 1927 and 1928 each refer to two post offices, although 
a report for 1927 indicated the Austrian post office was demolished in 1927 (Shaw 2003).
The new Italian post office
Early in 1927, the new Italian post office was built 1.4 miles from the cave entrance, more 
than twice as far into the cave as the old Austrian post office (Figure 2). Large and modern 
in style, with many tables outside beneath colored glass umbrellas (Figure 14), it was built in 
the southeast corner of the Concert Hall in Calvario not far from where today?s visitors catch 
the cave train back to the surface at the end of their tour. 
An Italian language guidebook of the same year (Postumia 1927) describes the post office. 
?On the right [of the Concert Hall], a vast cavity opens on this fine hall. The Post Cavern, in 
a pretty construction, also unique in its way, the postal service of the R.R. Grottoes is car-
ried on. All about, large umbrellas of colored glass, casting around a delicate light, invite the 
traveler to repose. From this point start daily thousands of postcards, with greetings from 
the unknown world (Figure 15).? 
Outside the cave, a newly constructed building opened on October 28, 1928, containing 
another post office as well as the ticket office, cloakroom, administrative offices, restaurant, and 
the station for the underground railway (Figure 6). The administrative office used the regular 
Postumia town postmark as well as the Postumia Grotte postmarks for its mail up to the end 
of May 1935 (Shaw 2003). It is likely that tourists? mail posted at the administrative building 
received it too, making the true underground mail indistinguishable for the next few years. 
Several administrative handstamps can also be found on postcards. It is not known if the 
Italian postal clerks applied these handstamps or if visitors used the handstamp and ink pad 
available to them at the counter (Figure 16). In June 1935, a new 31.5 mm diameter ?POS-
TUMIA GROTTE ? TRIESTE ?? postmark (Figure 17) was in use at the underground 
post office. 
Figure 14. The post office opened in 1927 in the Concert Hall. The illustration on the postcard 
shows a letter box on the far wall, a visitor writing at one of the tables with glass umbrellas, 
and a postal clerk standing in one of the three windows. Ufficio Postale R.R. Grotte (Official 
Postcard of the Royal Caves).
74 Thomas Lera
Between 1931 and 1939, Italy widely distributed a 
series of postal cards of different images of popular Ital-
ian places. These postal cards were specifically designed 
for tourism propaganda and for both internal (30c) and 
foreign (75c) mail. The imprinted stamp was an image 
of King Victor Emanuel III. Postumia Grotte had six dif-
ferent 30c postal cards, one of which is shown in Figure 
17 (Sopracordevole 1994).
The cave post office applied other markings to post-
cards and letters, like the ?T? for postage due (Figure 
18) and the ?Postumia Grotte Registration Label? for 
registered letters (Figure 19). 
After World War II
The Italian-built structure survived for many years 
after World War II, but for most of this time it was closed. 
When the cave was reopened to the public on August 
Figure 16. Administrative hand-
stamps (second from the top 
courtesy of Speleophilately Inter-
national) (Van der Pas 2001).
Figure 15. 1927 Italian language guidebook.
The underground railroad post office in Postumia Grotte 1872?1945 75
15, 1945, a special new red cave postmark (Figure 20) was 
used that day to cancel the first four stamps issued by the 
Yugoslav Military Government for use in Trieste Zone B 
of the former Italian-occupied part of Slovenia (The Istria 
and Slovene Coast) (Kloetzel 2006).
Figure 17. Italian Tourist card with a new cave postmark introduced in 1935 (31 ? mm di-
ameter).
Figure 18. Postage Due ?T? handstamp.
Figure 19. Postumia Grotte registered letter with 
cancellations and registration label.
76 Thomas Lera
Conclusion
Postumia Grotte is unique in having had 
an official underground post office (at one 
time two), which sold stamps and picture 
postcards that were accepted into the mail 
system. Authorized postmarks for the cave 
show dates from 1899 to 1945. The post office 
was included in the Universal Postal Union?s 
list of world post offices (Union Postale 
Universelle 1937), though not in all the later 
editions. The first building, erected around 
1899, remained in use until about 1927, when 
another was opened even further inside the 
cave. The old Italian-built post office was 
finally demolished in February 1983, so the 
present souvenir building could be erected 
before the tourist season began (Shaw 2003). 
Today the post office is located in the town of 
Postojna, with only a collection box outside 
the cave entrance. 
The underground railroad operated and serviced both post offices. Today, 130 years after 
the first double-seated carriages pushed by the cave guides were introduced into the cave, 
there are ten sophisticated battery-operated locomotives and six sets of carriages, two modern 
railway stations, one at the cave entrance and the other in Sala da Concerti, and a circular 
railway line (Shaw 2003).6 Now called Postojnska Jama, it is one of Slovenia?s world-class 
scenic highlights.
Acknowledgements
This work would not have been possible without the support of Alfred Kugel and Sandra 
Fitzgerald insights, comments and review. 
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Figure 20. Red ?POSTOJNA-JAMA? cancel 
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