The Acropolis is the most important ancient Greek monument, and one of the most important monuments in the world.
The Parthenon is a breathtaking temple that worshiped the cult of Athena the Virgin back then, and even though you cannot enter right now, you may still walk around the exterior.
The ancient amphitheater, also sometimes called Herodion, is still functioning until today even though it was built about 161 A.D. by Herodes Atticus, a Roman philosopher.
Large glass panes, a wonderful sense of space, light, and all shades of marble existing around you, bathed in UV light, make just wandering around the museum a fun experience.