Arguably the most awe-inspiring caverns in all of Europe, the Frasassi Caves are a staple of the Marche Region, which has a welcome lack of huge tourist reputation. The main cave, the Grotta Grande del Vento, is a massive stalactite and stalagmite filled space nearly a mile in the length of which is available for exploration.
Largely unmarred by human meddling, this limestone wonder is an hour's tour and fully worth the 15 Euros ($20 US). About three hours on the road from both Florence and Rome, this grotto is the epitome of off-the-beaten-path and a must for someone looking to combine the authentic Italian countryside with one of most attractive show caves in the country.
Note:Also, the cave is cool year round, so dress warmly.