One of the things you quickly get used to in Greece is that a theatre can turn up almost anywhere.
Even the smallest village might have its own ancient theatre. Not because the locals put on plays every evening, but because a theatre was, first and foremost, a place for watching.
The word theatre comes from the ancient Greek theatron. It literally means "a place for watching." Everything else came later.
The recipe for a classical Greek theatre is surprisingly simple: a hillside, semicircular rows of stone seats, and a stage below. No roof. No walls. Just a clear view and remarkable acoustics. Two and a half thousand years ago, people came here to watch tragedies and comedies. Today, it's mostly tourists wandering up and down the steps, whispering to each other to see if the echo still works.
Maybe that's why Greek theatres never really feel like museum pieces. They are still exactly what they were meant to be: places where people gather to watch something interesting.