The Imperial Palace until 1918, the Hofburg today, houses the office of the Austrian president, an international conference centre, a dozen museums, the chapel where the Vienna Boys’ Choir sing and the hall in which the Lipizzan stallions perform. Visitors can tour the Kaiserappartements (Imperial Apartments), including Franz Joseph’s and Sisi’s (Empress Elisabeth’s) private rooms, the great audience hall, dining rooms and staterooms. Schatzkammer (Treasury), at Schweizerhof 1, contains stunning exhibits that exemplify the power and wealth of one of Europe’s most important empires. The Sisi Museum showcases many personal objects and some of the most famous portraits of the beautiful empress. Also within the central core, the Prunksaal (State Hall) of the Nationalbibliothek (Austrian National Library) is a jewel of baroque architecture and one of the most beautiful historical libraries in the world.