Norse sagas mention the 13th-century fortress of Isegran, an islet in the Glomma that became a further line of defense against Sweden in the mid-17th century. The ruins of a stone tower are visible at the eastern end of the island. There's also a summertime cafe in the old powder magazine.
By road or on foot, access is from Rv108, about 600m south of Fredrikstad city center.
