You can tour the Opera House during the day and learn about its gorgeous architecture as well as enjoy a world-class performance in the evening. The opera house in Budapest stands as one of the most beautiful Neo-Renaissance buildings in Europe. When it was opened in 1884, the city shared the administrative duties of the Austro-Hungarian Empire with Vienna. Emperor Franz Joseph commissioned its design. Construction included the use of marble and frescos by some of the best artisans of that era. Designed by Miklós Ybl, one of Europe's leading architects in the mid to late 19th century, the Budapest Opera House quickly became one of the most prestigious musical institutions in Europe. Many important artists performed here, including Gustav Mahler!
http://visitbudapest.travel/guide/budapest-attractions/budapest-opera-house/