Castle Blankenheim, Medieval castle in Blankenheim, Germany.

Blankenheim Castle is a hill castle built around 1115 by Gerhard I above the village of Blankenheim in the Eifel. It was repeatedly remodelled, turning the medieval fortification into a Baroque schloss with a Baroque garden and an orangery. The site includes the Alte Palas, a southwest annex and a late-Baroque chancery building of 1786 in the lower castle.

The original fortress was founded in the early 12th century and served as the residence of the noble Blankenheim family for many centuries. After this ruling line ended, the structure changed hands several times before being adapted for a new purpose.

The castle gave its name to the House of Blankenheim, whose line died out in the male line in 1780; the estate passed to Count Philipp Christian von Sternberg, who had married Augusta von Manderscheid-Blankenheim in 1762 and called himself Sternberg-Manderscheid. Several women of the family served as princess-abbesses of Essen, and Karoline von Manderscheid-Blankenheim became Princess of Liechtenstein in 1783.

The castle now operates as a youth hostel and is primarily open to registered overnight guests. Those wanting to explore the interior should plan an overnight stay or inquire in advance about any daytime visiting options that may be available.

In 1469 Count Dietrich III of Manderscheid-Blankenheim had a tunnel cut through the ridge called Tiergarten so that spring water from "In der Rhenn" could reach the castle through a wooden pipe about one kilometre long; the castle had previously relied on rainwater collected in cisterns. The Tiergartentunnel was rediscovered in 1996.