This underground cemetary is one of the best preserved and most extensive Neolithic environments in Europe. It is believed to have been first dug in 4000 B.C. and used until 2500 B.C. It was rediscovered in 1902 and has been fascinating scholars and visitors ever since. The underground architecture in some of the areas is believed to mirror the Megalithic temples that would have stood above ground at the time. Look for the "echoing nook"—if you speak there, your voice will boom and echo out, a feature archeologists think was unswed in ancient ceremonies.