In Roppongi there's a store called Don Quixote which sold everything from cheap costumes for fancy dress to expensive and genuine Swiss watches. On the roof they built a roller coaster -- God knows to what purpose since there seems to be little access to the roof from inside, no space to queue and the roller coaster goes nowhere anyway. Never mind they didn't have planning permission to build it in the first place. To the best of my knowledge it's never been used.