...Amazing natural wonder... but the coolest part is that the postcard was sent from the only underground cave post office in the world with a special postmark....Thanks a lot Cendy!
The Postojna Caves started forming 3-4 million years ago with over 21 km of passages, galleries and halls, 13 are open to the public (since 1819). It is the most famous cave in Europe.
Postojna cave was visited by thousands of tourists, and therefore, the cave management sent a request to the Austrian trade ministry in Vienna for the opening of a post office in the cave.
On 15 August 1899, next to the Dance Hall, 500 meters from the entrance to the cave, the first underground post office in the world was opened.
With matching cave stamp.
The special cancellation shows the "Olm".
The caves are home to the (in Slovene) human fish or the olm (proteus anguinus), the largest troglodytic amphibian in the world.