The "Gigantic Cave" lives up to its name: 114m high, 924m long, and 65m wide (374 ft.*3,031 ft.*213 ft.), this single-chamber cave is the world's largest underground cavern open to the public. Warning: The requisite guided tours descend and ascend about 500 stairs total. Tours are in Italian, though if your group is mixed, they may play English and German recordings. The cave is about 15km (9 1/4 miles) north of the city near Opicina. An exciting way to get here is via the rickety tram that climbs into the hills from Piazza Oberdan (just west of the train station) and ends at Opicina, where you can catch the no. 42 bus to the cave. The tram runs every 20 minutes from 7:30am to 8pm, and the fare is 1.05€.