Blankenberg Castle, Medieval castle in Hennef, Germany

Blankenberg is a castle on a limestone hill in Hennef, built with thick stone walls and several defensive towers. The site offers views over the Sieg valley and shows typical features of a medieval fortified structure.

Blankenberg Castle was probably built between 1150 and 1180 and was first documented in 1181. In 1152 the Counts of Sayn, Eberhard I and Heinrich I, moved their residence here after giving up Sayn near Bendorf. In 1363 the castle, town and surrounding land passed to the Counts, later Dukes, of Berg. Swedish troops took and occupied it during the Thirty Years' War, after which it was partly dismantled.

Since 2006 the volunteer group Freundeskreis Burggarten Blankenberg has turned the bastion area into a herb garden holding over 200 medicinal and kitchen herbs, open whenever the castle is. Since 2012 the main castle has hosted the annual exhibition "Kunst auf Burg Blankenberg", showing mostly modern sculptures against the ruins. The name Blankenberg comes from the hill above the Sieg loop where the counts of Sayn settled.

Access is typically via a path leading up from the base of the hill, which requires some walking time. Visitors should wear sturdy footwear and be aware that older sections of the structure may have uneven surfaces.

The main castle is owned by the town of Hennef, while the outer bailey is private and cannot be visited. Since 2006 volunteers have turned the bastion area into a herb garden with over 200 medicinal and kitchen herbs, open whenever the castle is.