There are five islands of Koh Haa. The most famous Koh Haa Yai and Koh Haa Lek. They are part of the Mu Koh Lanta Marine National Park. Koh Haa Yai is the South and it is also the largest koh Haa island. In general people do not go to Koh Haa for the beach but to dive. Many divers like to visit the three main caves southwest of Koh Haa Yai. Two of them are inter- connected. The largest one is often referred to as the Cathedral. It makes the reputation of the place which is often listed among the most beautiful dive sites in Thailand. The cathedral is easily accessible through an from 6 to 13 meters opening. Inside, divers can surface and discover a breathtaking view over and around them. stalactites drop from the high ceilings and natural light filters through from the waters below, giving The Cathedral caverns a magical effect.
Around Ko Haa Yai, there are many species : leafy ghost pipefish, gorgonian sea fans, spiny lobsters in cracks, lion-fishes and if you're lucky, you can even sometimes see whale sharks. In April, whales pass by Koh Haa Yai for their annual migration.