One of the first of five publicly run leprosy sanatoria opened in 1909, Oshima Seisho-en is located on an island eight km east of the mainland Takamatsu pier and covers 61 hectares. At its peak more than 700 patients were admitted. As of December 31, 2015, it had 65 residents (former patients), with an average age of 82.5.

Setouchi Triennale festival includes Oshima island along with 11 other islands scattered in the Inland (Setouchi) sea area. It is an art festival, held every three years, since 2010, for 108 days a year, in three seasons. During the festival, more than 5000 people visit Oshima in a year. They learn about the history of the sanatorium and interact with some of the residents. It is a unique way to open the island sanatorium to outsiders and to sensitise visitors to the history of leprosy and to the people who have survived with it.

Oshima Seisho-en is served by five daily boat services that take 20 minutes to reach the island. These are provided by the government.