What is the official name of the building where Tokyo’s major sumo tournaments are held?

The official name of the building where Tokyo’s major sumo tournaments are held is Ryōgoku Kokugikan.

Ryōgoku Kokugikan, also called the Ryōgoku Sumo Hall, is the principal indoor venue for professional sumo in Tokyo. It stands in the Ryōgoku district of Sumida, an area strongly associated with sumo stables and history.

The present building opened in 1985 and replaced an earlier Kokugikan nearby. It is used for the January, May, and September honbasho, as well as other sumo events and ceremonies. The permanent indoor setting protects the tournament schedule from weather.

The venue is not the name of the city or the tournament itself. Tokyo is the host city, while Ryōgoku Kokugikan is the specific arena. The word kokugikan can be translated roughly as national sport hall.