I commented below with a similar idea. Like a public indoor park, for when Outside™ is no longer an option for recreation due to climate issues. They are big enough to accommodate large playgrounds, both child and adult style, running tracks, swimming pools, sports fields/courts. Keep the food court, sure, throw in a library, etc.
If we ever get a house and senate progressive enough to shave like 0.000000001% of the military budget we could put one in every abandoned mall and have funds left over.