"Kokugikan" (国技館) is a word to mean a facility which has a sumo field inside. It's a Japanese word consisting of "kokugi" (国技: national sport) and "kan" (館: museum, indoor arena).
In Tokyo, there existed / exists three kokugikan.
former Ryōgoku Kokugikan (ja: 旧 両国国技館): 1909 - 1940s
Ryōgoku Kokugikan(両国国技館,Ryōgoku Kokugi-kan?) is an indoor sporting arena located in the Ryōgoku neighborhood of Tokyo, Japan, next to the Edo-Tokyo Museum. It is the 2nd Ryogoku Kokugikan. The capacity of the arena is 13,000 people and it was opened in 1985. The first was opened in 1909. It is mainly used for sumo wrestling tournaments (honbasho) and hosts the Hatsu Basho in January, the Natsu Basho in May, and the Aki Basho in September. It also houses a sumo museum. The venue is also used for other indoor sports. In past years, it has hosted the G-1 Climax, an annual tournament in New Japan Pro Wrestling.