The underground hall is a new stage of the Bolshoi Theatre where music groups can hold rehearsals, including joint rehearsals of the symphony orchestra and the choir. First it was planned that in the hall located at the 15-meter depth, there will be held also concerts, but soon the idea was denied. And the main reason was the audience safety. One and a half year ago Yuri Luzhkov , the then mayor of Moscow strongly criticized the project of the underground rehearsal and concert hall developed by ZAO “Kurortproekt” and gave directions to commission “Mosproekt-2” to work on the project. The architect Pavel Andreev (who was running construction of the new stage of the Bolshoi Theatre) was commissioned to develop proposals and the project of the new audience zone interiors in the underground part under the foreground area of the Bolshoi Theatre for a new lobby and a rehearsal hall. The work on the project was started from changing the underground layout structure. The architects graded audience flows and provided access to the underground part from the main lobby, as well as from Petrovka street and Schepkinsky passage. The new lobby is located at the depth of 8 meters and has a system of staircases, lifts and escalators for visitors and providing services for visitors and various activities not just before and after a performance, but simultaneous festivities, presentations and exhibitions. Previously isolated space of the rehearsal hall now is transformed by portable soundproof screens and a tablet, divided into several segments, and thereby allowing to vary the level and the "profile" of the concert stage, creating conditions necessary to accommodate a large orchestra, an amphitheater for a chorus or rows of seats. Special mechanical equipment designed by Moscow engineers will not only make the “transformation” fast, but also absolutely safe for the audience – changing the floor level there will synchronically appear and exclude the possibility of falling into the forming gap.