The central space of the legendary Lucerna Palace is the Great Hall, which was completed in 1920 and at that time a very modern reinforced concrete construction. It consists of three underground levels, it’s 54 m long and 25.5 m wide, and can hold up to 4000 seats. The site is intended for the concerts of various musical genres, especially modern music. Many balls take place here as well.
Source: https://www.prague.eu/en/object/places/63/lucerna-palace-great-hall-palac-lucerna-velky-sal