What is in the Big Void?
Another intriguing discovery made in the Great Pyramid is a mysterious chamber with no apparent use. This chamber is called the big void. The chamber is called the big void because it is a large empty room, and it is not connected with any passages inside the Great Pyramid. This makes you wonder why the big void was built and why it was isolated from other chambers. Some speculate that it is to keep something in or prevent people from entering.
Source: Reddit
Scientists believe the chamber was built as a sort of support to the Pyramid; that is, to relieve some of the weight and prevent the Grand Gallery from closing in. Tourists can access the Grand Gallery if they hunch down through a long tunnel. The big void is almost equal to the Grand Gallery and sits directly above the Grand Gallery.