8. Aqualoop – Slovenia
At Terme 3000 water park, Aqualoop is one of Europe’s most extreme slides. After dropping through a trapdoor, riders speed into a full vertical loop — yes, like a roller coaster loop, but filled with water. You’re moving so fast that gravity alone takes you all the way around. It’s one of the few slides that truly flips you upside down. Short, sharp, and thrilling.