1. Seagaia Ocean Dome
Location: Miyazaki, Japan
The Tropical Islands Resort almost takes the cake but we cannot overlook the absurdity of the Ocean Dome, even though it is currently under renovation (there is no telling, if ever, it will be open again). It measures over three football fields in length and one across, has a fake flame-spitting volcano, and also holds the title for world's largest retractable roof. When the roof closes, it simulates a clear, blue sky. But that isn't event the best part.
The best part: This park is basically within pissing-distance of an actual ocean. Like, an outdoor, natural water park, with real sand, and real water, and all those other things.