Inside, there are halls, stadiums, and swimming pools. The main stadium is so large that it can seat 500,000 people. The giant swimming pools can hold 4,000 people all swimming at the same time and still have room for more.
If you walked around the Center you would wear your shoes out. So all traveling inside the building is done with elevators, moving stairs, and whole moving floors. Some of these are one-way, so it is important to remember which way you want to go.
Note: for a little context, I looked into stadium sizes. The largest stadium in the world is in Pyongyang, North Korea and seats 150,000. The largest in the US (#3 worldwide) is in State College, Pennsylvania and seats 107,282. So the stadium size proposed here is close to five times the size of this.
I’m unable to find how many people would fit in the world’s largest swimming pool, but based on the pictures, 4,000 doesn’t sound entirely off to me. It is incredibly enormous.