Château de Trémazan, Medieval castle in Landunvez, France.

Château de Trémazan is a castle ruin positioned on rocky terrain near the Breton coast, featuring a square central tower with four habitable levels. Thick defensive walls surround the structure, showing it was built to control and defend this coastal area.

The du Chastel family built Trémazan and made it their main residence for centuries. In 1220 it was destroyed during the war against the Duke of Brittany, then rebuilt about thirty years later by Bernard du Châtel. The present castle dates mainly from the 13th and 14th centuries; the first written mention is from 1351.

The du Chastel family held Trémazan as their main seat for centuries and ranked among the four leading families of Léon, remembered in a local saying pairing their bravery with the antiquity of Penhoët. The elder line died out for lack of a male heir at the end of the 16th century. In 1843 visitors noted red wallflowers on the ruins, which tradition links to the blood of Saint Haude.

The ruin sits on rocky coastal terrain and is accessible, though it offers limited facilities on site. A local preservation group organizes guided visits and maintains the structure.

A partial collapse in 1995 unexpectedly revealed internal chamber systems and architectural details within the main tower. This accidental discovery helped researchers better understand how spaces were arranged and used.