A couple very interesting articles about the miles and miles of underground Rome!!! Next time you are in Rome you should check out a few of these amazing places.
Here are a couple of articles to help you with Underground Rome
Our Ultimate Rome Tour includes amazing underground tours like San Clamente and the Catacombs!
(NOTE: Want Our Rome Cheat Sheet? Copy these done-for-you itineraries to make sure you see all of these amazing sights the right way. Get them here.)