Odeons are old concert halls that were popular in the 19th and early 20th centuries. They were typically large, ornate buildings with a central stage and seating for thousands of people. Odeons were often used for operas, plays, and other theatrical performances, as well as concerts. They were also used for political rallies and other public gatherings. The term 'ODEON' is derived from the Greek word for a building used for musical performances.