Sumo grand tournaments are held six times annually: in Tokyo, three times in January, May and September, in Osaka, once in March, Nagoya, once in July and in Fukuoka, once in November. I watched the Tokyo tournament(12th-26th of January, 2025) live in person.
The massive arena named "Ryogoku Kokugikan" accommodates 11,000 spectators. Recently, sumo has gained more popularlity all over the world so tickets will be sold out soon before the tournament. I applied for a pre-reservation online and got the ticket as a result of the lottery.