Tour d'Avalon, Medieval tower in Saint-Maximin, France.

The Tour d'Avalon is a tower of rough grey masonry blocks standing on the ruins of the medieval castle of Avalon in Saint-Maximin, Isère, and it reuses the base of the castle's former keep. Its upper part ends in a flat parapet with a low, slightly darker rim, and a thin metal rod rises just above that line. A vertical section of the same grey stone wall is exposed on its left side.

The tower was built in the late 19th century by Carthusian monks, who constructed it upon the foundations of an earlier watchtower structure. The earlier fortress belonged to the Romestang d'Avalon noble family, which once ruled the area.

The tower is named after Saint Hugh of Avalon, bishop of Lincoln from 1186 to 1200, who was born at the castle that once stood here. The Carthusians of the Grande Chartreuse, whose mother house lies in the same Isère department, built the tower in 1895 in his honour.

The tower stands on the ruins of the medieval castle of Avalon in Saint-Maximin, Isère, on the site of the former keep; the surviving masonry is rough grey stone with a flat parapet. The site is a listed monument historique since 5 October 1992, so access is not organised as a staffed attraction and there are no guided facilities on site. Approach on foot from the village and check locally before planning a climb.

The tower keeps the footprint of the keep of a castle held by the Romestang d'Avalon family before 1049, and its site is linked to Hugh of Avalon, bishop of Lincoln from 1186 to 1200. The Carthusians built the present tower in 1895, and it was listed as a monument historique on 5 October 1992.