From Grand Sumo: The Living Sport and Tradition, rev. ed., by Lora Sharnoff (Weatherhill, 1993), pp. 67, 69:
The present Kokugikan in Ryogoku, where three of the tournaments are held annually, serves as the headquarters of the Sumo Association. The stadium is a 35,342-square-meter building with a seating capacity of 11,908; it stands 39.6 meters at its highest point. It has three floors aboveground and two underground. The stadium was constructed to withstand earthquake tremors up to ten on the Richter scale and is equipped with computerized temperature control, fire prevention equipment, and sensors to detect gas leaks. It also has a 1,250-ton tank designed to store rainwater and divert it to the toilets and air-conditioning system inside….
On the second floor the seats are Western-style chairs. However, except for some tables with lounge chairs in the very back, the first floor is given over to traditional Japanese seating arrangements on tatami…. The first five rows around the ring are individual seats called tamari-seki or suna-kaburi. The latter, meaning “sand-covered,” comes from the fact that spectators sitting in this area occasionally take in some of the sand kicked up on the dohyo or flying off the body of a falling rikishi. Despite the unglamorous appellation, the suna-kaburi are the most sought-after seats….
The seats as well as the tickets are labeled shomen (main side), muko-jomen (opposite main side), higashi-gawa (east side), and nishi-gawa (west side). The present labeling in the Kokugikan is actually the opposite of the actual compass points and traces its origins to the tradition of the emperor always sitting facing south. The area in which he sat was designated the main or northern side, and everything to his left was deemed the “east side,” and to his right the “west side”—a pattern which can be seen in the old capital of Kyoto. Thus, what is supposed to be west from his perspective is actually east on the compass, and vice versa. In the Kokugikan the emperor’s box is actually located on the second floor in the middle of the building’s southern side, which in respect to tradition is called the main or northern side.