Enhancement project of the Telesterion at Eleusis underway
The temple complex at Eleusis was one of the most elaborate and widely used sanctuaries around in ancient Hellas. It was the home of the Eleusinian Mysteries, and thus served as the cult's sanctuary. Like many--if not all--ancient monuments, the ancient temple site of Eleusis has not withstood the test of time and humanity particularly well; foundations remain, but much of the grand complex is completely gone.
One of Eleusis' grand features was a large hall, capable of housing thousands by the 5th century BC. The hall, known as the Telesterion served as the key hall for the Mysteries; here the initiates were shown a reenactment of the events that led to the founding of the Eleusinian Mysteries in the form of an elaborate dance, and they were shown the sacred relics. Anything that hppened at the Telesterion was considered especially secret, and the punishment for revealing what went on in the hall was death.
http://baringtheaegis.blogspot.nl/2013/07/enhancement-project-of-telesterion-at.html