This is what we found on Wikipedia regarding the State Theatre Guided Tours:

The Hungarian State Opera House (Hungarian: Magyar Állami Operaház [ˈmɒɟɒr ˈaːlːɒmi ˈopɛrɒɦaːz]) is a historic opera house located in central Budapest, on Andrássy avenue. Originally known as the Hungarian Royal Opera House, it was designed by Miklós Ybl, a major figure of 19th-century Hungarian architecture. Construction began in 1875, funded by the city of Budapest and by Emperor Franz Joseph I of Austria-Hungary, and the new house opened to the public on the 27 September 1884. Before the closure of the "Népszínház" in Budapest, it was the third largest opera building in the city; today it is the second largest opera house in Budapest and in Hungary.

Touring groups had performed operas in the city from the early 19th century, but as Legány notes, "a new epoch began after 1835 when part of the Kasa National Opera and Theatrical Troupe arrived in Buda". They took over the Castle Theatre and, in 1835, were joined by another part of the troupe, after which performances of operas were given under conductor Ferenc Erkel. By 1837 they had established themselves at the Magyar Színház (Hungarian Theatre) and by 1840, it had become the "Nemzeti Színház" (National Theatre). Upon its completion, the opera section moved into the Hungarian Royal Opera House, with performances quickly gaining a reputation for excellence in a repertory of about 45 to 50 operas and about 130 annual performances.

Today, the opera house is home to the Budapest Opera Ball, a society event dating back to 1886.