The most reputation of Lanta is the dive sites. 

Hin Daeng & Hin Muang were rate from international dive magazine as world top ten diversity sites.

Hin Daeng or Red Rock is a huge pinnacle protrudes three meters above the surface. The east side is shallower with two long narrow ridges gentle slope in to the blueness, pleasing with lush red soft coral. The southern of pinnacle fast drop as the huge wall dotted with soft coral and sea fans.

Hin Muang or Purple Rock is just a few hundred meters away, the underwater rock is about 200 meters long and narrow round top with two side wall. The site is pleasing with lush purple soft coral insertion with large sea fans of red, white and orange. Both sites often found large schools of jack tuna, large size barracudas, gray reef sharks, huge needle flying fish and long toms and sometime huge whale shark and manta ray.

Koh Ha is a group of five tiny islands west side of Koh Lanta. The interesting is the series of underwater caves look like a cathedral. At Koh Ha Yai the caves are very complexity. The main cave is safe to enter; look back will see the lighting pipe passing through the hole of chamber is illusion. Penetration into the passage way at the rear of the main chamber is dangerous and it is not recommended.

The other sites are as Hin Bida , Shark Point and Ship Wrack which more near to Phi Phi island but easy access from Koh Lanta.