Any property currently for sale in Pennsylvania. With money left over to play with unless you're an idiot and buy a $15m condo in Philly, which would make you the dumbest person in the state.
A quarter of an island for sale in Florida at the moment.
Although there is an old race track for sale a mile from me for a million. 28 million might make it useable again.
If you're ever really bored, without 28 million to spare, hop on zillow, punch in a state, and minimum price 5 million. It's interesting to see what you can buy where.