Mont-Saint-Michel

A church sits on the summit with three halls propped under it, so rooms lighten as you climb. Two rows of cloister columns stand out of line, so walking past makes them close and open. From May to August it opens in the evening too, lit for a night visit.

There is one main street on the island and it takes two people abreast at best. Souvenir shops line both sides, and once you are in that file, turning back is hard. Opening hours differ shop by shop, so early on about half stay shuttered.

The tidal range here is among the largest in Europe. At low water the flats appear; at high water they vanish. The 2014 bridge stays walkable all year. Only tides over coefficient 110 put the esplanade under for an hour or so, on published dates.

Do not walk onto the flats without a guide. Under standing water sit mud pools that swallow a leg. You are told to go barefoot in shorts, and the start time is set by the tide of that day.

A large wooden wheel survives from the years after the Revolution when this was a prison and inmates walked inside it. A rope from the wheel hauled a sledge of supplies up the slope.

A small church for the village, kept apart from the abbey, with a silver armoured figure by the door. The graveyard beside it steps down the slope in tiers because there is so little ground.

A walk along the top of the walls runs parallel to the main street and gets you up without the crush. Towers open the view over the bay, and the stair is too narrow for two-way traffic.

A rock rises out of the flats to the north, now a bird sanctuary that nobody is allowed to climb. In spring and summer gulls and cormorants cover the stone until it reads as a white stain.

A barrage at the river mouth holds water back and lets it go in one rush to scour out the sand. Without that the flats silt up and the rock joins the land. It has run since 2009, and you can walk across the top of it.

A broad stone terrace in front of the abbey church with nothing at all to break the wind, which has you fastening your coat.

Opened in 2014 in place of the old earth causeway, it lets water run underneath so the island is ringed by sea again. From the car parks you take the shuttle or walk nearly 3 kilometres. On the very highest tides its far end can go under.

In hilltop Avranches across the bay, this museum shows medieval manuscripts the abbey's monks copied. The nearby Saint-Gervais basilica holds Bishop Aubert's skull, pierced, legend says, by the archangel's finger. Together they fill half a day.

A walled port about an hour's motoring west, once base to royal-licensed privateers. On the rampart walk, sea and old-town roofs take turns. At low tide a sand bar leads to Chateaubriand's grave on Grand Be; misjudge the tide and you are stranded.

An oyster town on the bay's far west side, where low tide bares endless rows of oyster beds. Stalls on the harbour wall open a plate for you, you eat on the wall, and the shells get thrown onto the shore below. That is why the beach beneath is made of them.