I once checked out a similar basement apartment for a friend. There were three or four bedrooms within this basement, taking up maybe 30% of the total basement square footage. The rest was absolutely unusable open space with tons of support beams breaking it up, and an extremely slippery granite floor. The kitchen was nice and you could theoretically see the TV in the "living room" zone, but it was like 30-40 feet away so it was too far to be useful.
Just a big ole batcave under a giant home.