You are standing at the edge of a very big, very empty room. The place is colossally huge, being almost ten times bigger than all of the other places in Andy's brain put together, and yet there's virtually nothing in it, just bare concrete floor stretching off into the distance. The only thing here is a small sign that says "This is the other 90% of Andy's Brain, which he is not currently using." Under this is a smaller sign that says "For Rent."
The only way out of here is back the way you came in. Or you can look at the map.