Athens, Greece: Theatre of Dionysus

It's easy for a structure to be overlooked and overshadowed when it is next to the top of the Acropolis. After all, the buildings are huge and impressive to this day. But don't overlook what's there to say on the way up or down, depending on your direction. 

The Theatre of Dionysus has a huge amount of cultural significance. It was built in the sixth century BC, and is considered to be the first theatre ever built. This is where Greek tragedy was more or less invented. 

When Rome took over the region, the wood seats were gone and marble was put in its place. The facility may have held as many as 17,000 people at a time (another source put capacity at 25,000). The theatre was overlooked for a while, as other buildings were placed on top of it. That changed in the 1700s, and formal exploration of the site began in 1838.