Blens Castle, Medieval castle in Heimbach, Germany.

Blens Castle is a medieval fortress that rises on a hilltop above the River Rur in the Eifel region. The structure features a quadrangular layout with residential buildings made from rubble stone and a two-storey manor house, its courtyard paved with historic river pebbles.

A seal of Johannes de Blens records the family at the start of the 12th century; their male line died out in 1380. Through marriage the hill castle passed to the von Berg family, extinct in 1550, then via the Freiherrn Raitz von Frentz in the 18th century to the Beissel von Gymnich. In the 20th century it came by marriage to the von Abercron family, who own and live in it today.

The castle is privately owned and inhabited by the von Abercron family, who acquired it in the 20th century through Georg Anton Beissel von Gymnich. It is not open to visitors; the Chapel of St. George stands just to the northwest of the site.

The castle is privately owned and lived in by the von Abercron family, so the grounds and manor house are not open to visitors. The site stands at 205 m above sea level on the eastern edge of Blens, above the Rur, and can be viewed from the surrounding village lanes and paths. The Chapel of St. George lies immediately to the northwest.

A 1723 document, the Welser Codex, depicts the castle with a triangular outer ward and stepped gables, suggesting significant architectural changes occurred. This historical illustration differs noticeably from the structure today, raising questions about how parts of it were rebuilt or simplified over time.