Seiryu-en garden of Nijo Castle, World Heritage Site in Japan. Nijo Castel is a flatland castle located in Kyoto, Japan. The castle consists of two concentric rings of fortifications, the Ninomaru Palace, the ruins of the Honmaru Palace, various support buildings and several gardens. The Seiryū-en garden is the most recent part of the Nijō Castle. It was constructed in 1965 as a facility for the reception of official guests of the city of Kyoto and as a venue for cultural events. Seiryū-en has two tea houses and more than 1000 carefully arranged stones.