Sottomarina (ソットマリーナ Sottomarīna?) is a frazione, or ward, of the comune of Chioggia, which is part of the province of Venice in the Veneto region of northern Italy. It is far away from the central town where Orsola Aquinas lives.
In Toaru Majutsu no Index, it is the short stopping place for Touma, Index, Lucia, Angelene, Orsola, and the rest of the Amakusa Christians after the ice ship of La Regina del Mare Adriatico that Touma was on was destroyed. Here, they discuss what they'll do to save Agnese Sanctis from La Regina del Mare Adriatico over the course of dinner.