"There are deep caverns and fissures"
by cm
Timisoara Cave
Creative Commons AttributionTimisoara Cave - Credit: Francisco Gonzalez

There are indeed some fine caves in Transylvania.  Romania as a whole boasts over 12,000 caves, many of them in the Carpathians.

For the adventurous who want to explore them, here are a couple of options:

Outdoor Holidays  Green Mountain Holidays

 

Muierilor Cave
Creative Commons AttributionMuierilor Cave - Credit: Cristian Bortes