Falkenstein Castle (German: Burg Falkenstein) is a ruined hill castle near Freiburg im Breisgau on the territory of the present-day municipality Breitnau in the county of Breisgau-Hochschwarzwald in the German state of Baden-Württemberg. The castle site lies in a triangle formed by the entrance of the Höllental valley – the Lower Höllental and the Engenbach valley, not far from the Buchenbach village of Falkensteig, 617.6 m above sea level (NN) on a rocky crag that is very difficult to get to today. Of the castle itself only a few wall remains are left. It is one of the less well preserved ruins in the Breisgau.