I have to go with Coral Castle.
With a name like that, you’d think it will be related to the sea or found near the coastline. Is actually surrounded by modern infrastructure in the middle of Miami. Stepping inside feels like you entered a new world, a private city oblivious to its surroundings. Only the crowds of visitors and tour guides explaining its history remind you that you’re still in Miami, Florida (don’t let the picture fool you, the place was packed). The mystery of how and when it was built further accentuates its sci-fi aspect.