Kastelberg, Mountain summit in Vosges, France

Kastelberg is a grass-covered summit in the Vosges, reaching 1,350 metres, the fourth highest in the range. Its rounded top forms a long, smooth crest above slopes clothed in darker green forest, with a lighter clearing and a path cutting through the trees on its western flank. The summit marks the old regional boundary between Alsace and Lorraine.

The mountain sits in a region once divided between Alsace and Lorraine, a boundary that shaped settlement patterns and trade routes. This division influenced how communities developed on either side of the border.

The name Kastelberg comes from German and means "castle mountain", though no castle stands on the summit. The mountain marks the old regional border between Alsace and Lorraine, and its slopes are shared by the communes of La Bresse and Metzeral. A locality called Schwalbennest, German for "swallow's nest", is known for holding snow late into the year.

The summit can be reached by hiking trails from Col du Calvaire parking area or by ski runs from La Bresse resort depending on the season. Plan your visit around weather conditions, as snow and fog often cover the upper slopes.

The snowfield at Schwalbennest, a locality of Wormsawald-Ammelthal, is the most persistent in the Vosges, usually lasting until July and sometimes August; in 1978 it survived until 15 September. Its name means "swallow's nest" in Alsatian and German.