Thailand's Andaman sea coastline is shorter than the Gulf of Thailand coastline, but is dotted by countless islands and islets. A characteristic feature of this area are karst rock formations, with steep coastline and mushroom-like rocks emerging from the sea. Thailand's biggest island along this coast is Phuket, which attracts a large number of tourists. The area around Krabi is popular with backpackers. Rai Leh beach is a major rock climbng centre.