We set out early to find the allee couverte du Bois-Couturier near Guiry-en-Vexin. They have maps to show you how to find it at the prehistory museum in Guiry. You have to walk about 20 minutes through a forest, on reasonably good clearly marked paths, to find it. But when you have you'll love it!
It was rediscovered in 1915 and excavated until 1919: 200 skeletons found as well as polished stone axes, tools and ceramic shards. It's 8 ms long and 2 ms wide – I thought the proportions seemed quite odd compared with many allee couvertes we'd seen. Essentially it's a sunken box entirely lined with drystone walling and covered with 4 capstones.
The most astonishing thing about it is the round and lovely porthole in the portal stone – quite perfect! I crawled through it and into the tomb. I sat inside to consider that that the round blocking stone 'door' was discovered during excavation, and in superb condition. It now lives in the nearby prehistory museum. It looks like a great saucepan lid, complete with handle.