Ryogoku is an area where one of the most popular sports in Japan, sumo wrestling, is located. I didn't fully understand the popularity of sumo until I watched news on television in Japan. They always end the news hour with sumo and baseball information.
Kokugikan Sumo Stadium first opened in 1985. It seats over 10,000 visitors and hosts three of the six annual sumo tournaments in January, May, and September. On my visit to Ryogoku, I walked around and discovered it was quiet and deserted, but I could see many sumo-related objects around. For those who are interested in sumo, there is a special sumo museum nearby that is free of charge.
In Ryogoku, there is also: Yokoamicho Park, Tokyo Memoria Hall, a temple, few museums, and a small but nice Japanese landscape garden called, "Kyu-Yasuda Taien." It has a small pond with turtles and birds, such as the heron. From Ryogoku, you can walk farther along the Sumida River to see other famous areas such as the Skytree town and Asakusa.