More recent in construction (161 AD.) than the Theater of Dioysseus and better preserved, the Odeon of Herodes Atticus is still in use today but unfortunately only holds 5,000 spectators. Only the lower tier of seats remain.
Like most Greek Odeon's it has superb acoustics. Odeon's are a separate type of construct than theaters in that most had a wooden roof for acoustic purposes. This very roofs susceptibility to fire is what makes them scarce today. This Odeon's ceiling was originally of rare Lebanese cedar wood and particularly expensive.
Herodes Atticos, a philanthropist, was also a famous Greek orator, and very rich and liberal. He donated the theater to the city in memory of his wife Appia Annia Regilla who was Roman and a cult preistess.