The Château de Blain or Château de la Groulais, is a mediaeval castle constructed in the 13th century and heavily remodelled in the 16th, located in Blain.
The castle stands on the side of the Nantes to Brest canal It has 12 towers and covers an area of 4 hectares.
The castle suffered further serious damage during theFrench revolution. It was pillaged and burnt, along with the Rohan family archives. It served as a barracks and later as a prison.