Trulli are limestone dwellings found in Alberobello and the southern region of Puglia. They are remarkable examples of drywall (mortarless) construction, a prehistoric building technique. Alberobello is a UNESCO World Heritage Site. 
More Information on Alberobello and Trulli from the About.com Guide to Italy Travel
Alberobello (c) Linda Garrison
There are even trulli you can stay in. I stayed in a trulli hotel last spring, very unique.
Thats a really great picture, Puglia really is a fantastic part of Southern Italy. Did you know that the Puglia region produces 80% of Italy’s olive oil !