This royal temple was built in the reign of King Rama III in 1846. It is famous for its Loha Prasat (Metal Castle) standing to the west of the main temple. It is square in shape with 3 storeys and 37 spires, which symbolize 37 qualities contributing to enlightenment in Buddhism. Inside this chedi is enshrined an urn containing relics of the Buddha. Despite its name, there is no metal part in the whole structure except the lightning rods fixed to the pagoda tops. Presently, it is the only one of its kind left in the world. (The two formerly built in India and Sri Lanka were already in ruins.) There is also a museum located at the ground floor of the castle.