Hypogeum architecture

The Hypogeum of Paola, Malta, literally meaning "underground" in Greek, is a subterranean structure dating to the Saflieni phase in Maltese prehistory. Thought to be originally a sanctuary, it became a necropolis in prehistoric times. It is the only prehistoric underground temple in the world. The Hypogeum was depicted on a 2 cents 5 mils stamp issued in the Maltese Islands in 1980 to commemorate the acceptance by UNESCO of this unique structure in the World Heritage Site list. It was closed to visitors between 1992 and 1996 for restoration works; since it reopened only 80 people per day are allowed entry.

• http://en.wikipedia.org/wiki/Hypogeum of Ħal-Saflieni