I was last in Cornwall in summer 2014. A visit to the tidal island of St. Michaels Mount was one of my absolute highlights. The path to the well-preserved monastery building, which looks like Mont Saint-Michel in France, is only passable at low tide. When the tide comes in, boats have to be used. To this day, a handful of people live on the island and depend on the tides for their daily lives.
I'm looking forward to packing my bags again.