Beautiful region with incredible tides and a magnificent Abbey (construction started in 709). The architecture of the Abbey and how it was constructed is marvelous. See also this general narrative and well illustrated document (in French). About the history of the development of the building, I found this document (in French) that illustrates the different elements of the architecture, it is so, so impressive.
Selected picts: view of the surroundings (low tide), the gates to the citadelle, contructions around the Abbey and the inside of the Abbey (I did not document what room is what (but see the links provided above ;-).
The treadmill was operated by prisoners after 1793, when the abbey was turned into a prison. It was used to bring supplies and other material in the Abbey. The prisonners were volunteers to walk the mill.