The Camp d'Artus is a Gaulish hillfort on the edge of the Huelgoat forest, its ramparts still visible in the landscape — earthwork ridges through the trees that you might mistake for natural contours until you follow them and realise they form a deliberate enclosure. The site dates to the Iron Age and was occupied when Julius Caesar was pushing through Celtic Gaul.
It is a 30-40 minute walk from the village centre, and the path to get there takes you through the quieter parts of the forest beyond the main boulder circuit. Most day-trippers don't make it this far, which means you often have the hillfort to yourself.
The name comes from medieval Arthurian legend, which liberally attached the king's name to ancient earthworks across the Celtic world. The site itself cares nothing for this — it is a piece of genuine, pre-Roman Brittany, and worth the extra walk.