Thailand's water experiences are among the best-organised in Southeast Asia. Phang Nga Bay sea cave kayaking — paddling through limestone cave tunnels accessible only at low tide into hidden lagoons (hongs) inside the karst towers, inaccessible in any other way — is the most specifically Thai water experience available. Railay Beach longtail boat excursion circuit in Krabi, Similan Islands liveaboard diving expeditions to the Richelieu Rock whale shark site, and Chao Phraya River express boat tours between the ancient temples of Bangkok add the coastal and river registers. Khao Sok Lake floating raft house boat tours through drowned forest in the Cheow Lan Reservoir, Mekong River slow boat journey from Chiang Rai to Chiang Saen along the Thai-Laos border, and Koh Tao marine conservation snorkel boat excursions complete a water programme of exceptional variety.