The state's only drive-in beach, Muzhappilangad in Kannur, which stretches across five kilometres of sand, was chosen by the BBC as one of the top six drive-in beaches in the world in 2016. Idukki Dam, the world's second arch dam, and Asia's first is at Idukki. The major beaches are at Kovalam, Varkala, Kozhikode, Fort Kochi, Cherai, Alappuzha, Payyambalam, Kappad, Muzhappilangad and Bekal. Popular hill stations are at Ponmudi, Wayanad, Wagamon, Munnar, Peermade, Ramakkalmedu, Paithalmala of Kannur district, Kodikuthimala, and Nelliampathi. Munnar is 4,500 feet above sea level and is known for tea plantations, and a variety of flora and fauna. Kerala's ecotourism destinations include 12 wildlife sanctuaries and two national parks: Periyar Tiger Reserve, Parambikulam Wildlife Sanctuary, Chinnar Wildlife Sanctuary, Thattekad Bird Sanctuary, Wayanad Wildlife Sanctuary, Muthanga Wildlife Sanctuary, Aralam Wildlife Sanctuary, Eravikulam National Park, and Silent Valley National Park are the most popular among them. The Kerala backwaters are an extensive network of interlocking rivers (41 west-flowing rivers), lakes, and canals that centre around Alleppey, Kumarakom and Punnamada (where the annual Nehru Trophy Boat Race is held in August), Pathiramanal a small island in Muhamma. Padmanabhapuram Palace and the Mattancherry Palace are two nearby heritage sites. Padmanabhaswamy Temple in the state capital of Thiruvananthapuram holds the record as the wealthiest place of worship in the world, with assets of at least .