Ar Men ("the rock" in Breton) is a lighthouse at one end of the Chaussée de l'Île de Sein, at the west end of Brittany. It shares its name with the rock on which it was erected between 1867 and 1881.
Ar Men is one of the best known lighthouses because of its isolated situation and the considerable difficulties its construction has presented, and the danger in evacuating its personnel. Considered as one of the most challenging workplaces by the community of lighthouse keepers, it has been named "The Hell of Hells".
The light was automated and electrified on 10 April 1990 with a 250 watt halogen lamp. Its signal is three white flashes every twenty seconds, with an accompanying signal of three sounds every sixty seconds.