The phrase "main hall" refers to the largest or most important room in a building or facility where events, gatherings, or important activities usually take place. Full definition
European style breakfast is served in the room and you will get complimentary cocktails during the evening in the library and main hall of this hotel. (gomonterey.com)
The entire main hall could be a wood replica. (treehugger.com)
Along with blackout conditions and hazy air to help make light beams discernible, the vertical works call for more than 30 feet of height to traverse — a necessity that the enormous main hall at Pioneer Works can match. (artnews.com)