Ko Lanta Yai is in the Andaman Sea off the west coast of Thailand, between the Phi Phi Islands and the mainland. It comprises 52 islands in the southernmost region of Thailand's Krabi Province, of which the largest and best-known is Koh Lanta Yai.Friendly locals and its unspoiled nature are still ma See more.in attractions. Misty mountains abound in some areas, especially down south, while the islands' lush jungle, clean sandy beaches, pretty coral reefs and crystal-clear water make for a relaxing retreat.. Hide this content