Lazio is the area around Rome. It has two geologically and geographically different parts.
Around Rome, the flat lands of the river Tiber, the coastal plains, and the hills are rather young. The hills were formed by a series of gigantic volcanic eruptions around the Albani Hills. The most obvious signs of this volcanism are the circular crater lakes Lago di Boldesna and Lago di Bracciano, and the numerous spas in this area. There are no natural caves in this are, but the long history of Rome is the reason for a vast system of underground structures. There are numerous underground sites of any imaginable category, which are open to the public.
The second, much older part is a chain of calciferous mountains, running roughly parallel to the main Apennine range, called Appennino Abbruzzese. This area it very interesting for cavers, as the limestone is karstified. The caves of this area lie all in this area.