Location: Budapest, Hungary
Perhaps the least likely, yet somehow least surprising, location for an indoor water park is Budapest. The city is divided by the river Danube (the east side is Buda and Óbuda with Pest on the west, united in the late 1800s) and home to natural hot springs. This park is outside the city and thus takes no part in the hot springs. But it does have a large replica of a Cambodian Angkor Temple. Who needs hot springs anyways?