Pepper Pot

The British built 15 Guernsey loophole towers at various points along the coast of Guernsey between August 1778 and March 1779 to deter possible French attacks after France had declared itself an ally of the Americans in the American Revolutionary War. Towards the start of the Napoleonic Wars several towers received additional reinforcement in the form of batteries at their bases. Today, 12 towers still survive, three having been destroyed at different times. Two of the survivors, Petit Bôt and Rousse, contain interpretive exhibits that the public may examine.

Source: Wikipedia