I think patrice has gone full terrain tiles
We use 32mm thick tiles (not so thick on the sea coast and river banks). Also, an other idea we had for a game, we made a few card sheets, painted and sand-covered, as this one. The idea was to simulate the tide effect.

When the game begun, the two players who were supposed to reach the place with their boats were unhappy to see it and said "that's stupid we cannot enter the place, etc." and the GM answered: just wait for the tide (and then the sand was removed).
