The Cathedral

The Cathedral is an underwater limestone cavern on Koh Haa Yai known for a large high-ceiling chamber with hanging stalactites and multiple linked caverns and swim-throughs that are illuminated by sunlight filtering through the water, creating a cathedral-like glow. The dive follows the coral reef slope on the southwest side of the island into tunnels and swim-throughs; depths range from about 6 m at the cave entrance to 20-25 m on the reef slope, with swim-throughs at 8-10 m and the deepest part of the cathedral chamber reaching about 30-36 m. Visibility is often around 20-30 m and water temperature is steady at about 28 °C year-round. The site is boat-access only; Koh Haa Yai has no shore entry. Currents are generally moderate but can be strong on the exposed side and drift dives may occur. Parts of the route pass through an overhead environment with a single underwater surface entrance/exit, so good buoyancy control and experience with caves or swim-throughs are recommended.