Many moons ago I visited Jersey (the one in the English Channel). One of the many highlights was visiting La Corbière[1], a lighthouse only accessible via a causeway that is submerged at high tide[2, 3]. Fascinating place.
[1] https://en.wikipedia.org/wiki/La_Corbi%C3%A8re
[2] https://www.google.com/maps/@49.1806882,-2.2470043,3a,75y,22...
[3] https://www.google.com/maps/@49.18135,-2.2449889,3a,75y,243....