Château Saint-Léon, Medieval castle in Eguisheim, France.

Château Saint-Léon is a fortified castle in Eguisheim with an octagonal floor plan, a central keep, and thick stone walls from the 13th century. The structure displays features of medieval military architecture and remains open to visitors today.

The castle's oldest masonry dates to the first half of the 13th century; its octagonal ring wall of yellow and pink sandstone, about 1.8 m thick, points to the counts of Dagsburg or the bishops of Strasbourg as builders. The first certain written mention is a Strasbourg property register from the time of Bishop Johann I. In 1226 Bishop Berthold bought the margrave of Baden's rights over Eguisheim. From 1348 the whole complex belonged to Hans von Zellenberg, bailiff of Eguisheim.

The neo-Romanesque chapel, consecrated on 17 May 1894, was built between 1886 and 1895 to designs by Charles Winkler as a memorial to Pope Leo IX, replacing the demolished central keep. Recent research has undermined the long-held claim that the pope was born in this castle. The chapel is usually open to visitors and occasionally hosts religious services.

Visitors can access the grounds and interior spaces that are sometimes used for exhibitions and official events. Wearing comfortable shoes is recommended since the terrain is uneven and you will walk through old stone structures.

The octagonal enceinte, about 13 m per side and 1.8 m thick, is built of yellow sandstone bossage below and pink sandstone above. Excavations in 1994 and 1995 found no traces older than the 13th century, and the keep's foundation, uncovered in 1908, was reburied. The wall was cleared of lean-to structures and restored in 1908, then again in 1988–1989.