Fort de berthume

Near our France house swap was fort de berthume. We had walked past it before when it was closed but we went to it again and visited it and it was open. The fort had been continuously occupied all through ww1 and 2 and before that, so it had a bunker with a secret passage to the shore. You could also do zip lining across ocean rocks and a large gap, but we saw some other people do that so we didn't do it because it looked scary.