The Townsville City Opera House, is mentioned, and briefly shown the inside of in the episode "The Powerpuff Girls: Dance Pantsed". Not much is seen of it, nor much information is known about it. However, Wendy Bags used it in the episode before being kindnapped by Mojo Jojo.
This could be the same opera house that's briefly shown in the episode Daylight Savings.
Possibly the same opera house is also briefly visible (and destroyed) during Not So Awesome Blossom.