As of 2026, Sandcastle Waterpark in Blackpool maintains its title as the UK's largest indoor waterpark. It features 18 slides and attractions, including the "Master Blaster," which is the world's first uphill water rollercoaster. The park is famous for its tropical 84°F climate, making it a year-round destination regardless of the British weather. However, if you are looking for the largest outdoor waterpark, that title often goes to Aqua Park Rutland, which covers over 8,000 square meters of a reservoir with inflatable obstacles, climbing walls, and massive slides. In 2026, competition is fierce, with The Wave in Coventry offering some of the most technologically advanced high-speed indoor slides in Europe. For travelers in the north of England, Alpamare in Scarborough also offers a massive hybrid experience with both indoor and outdoor heated infinity pools. For sheer volume of attractions under one roof, Sandcastle remains the record-holder.