Tucked beneath the earth's surface you'll find the Postojna Caves, a massive cave system that boasts a fantasyland of breathtaking stalactites and stalagmites carved by the Pivka River over millions of years. Your adventure begins with a relaxing coach ride from Trieste to Slovenia. When you arrive at the cave, you'll board the world's only double-tracked cave railway. Imagine the thrill of discovery when you encounter a surreal landscape of limestone karsts that were created eons ago. During the 90-minute tour, you'll ooh and aah over the surreal setting and view the spectacular terrestrial phenomenon called the Skyscraper-a 16-meter-high pure white stalagmite that's estimate to be 150,000 years old. You'll also see the world's oldest underground post office in the world and, if you look carefully, the olm-a pale blind eel-like salamander that lives in these waters.