A visit to Fort Grey on Guernsey shows a Martello Tower and nearby fortifications built by the Germans in their WW2 occupation.
Visiting Fort Grey
The Martello Tower attached to the fort now houses the Maritime Museum and it is open to visit in the summer. Information in the link below.
My Experience
As our visit was in February 2012 there was nothing actually opened but the whole coastline has defences from various eras to see.
Fort Grey Photo Gallery
History
The Fort is located on a small tidal islet in Rocquaine Bay on the west coast of Guernsey, connected to the shore by a raised causeway. It stands on the site of an earlier small castle, the Château de Rocquaine and is now known affectionately as the “Cup and Saucer”.
It was built in 1804, as part of a chain of defences built to protect Guernsey against the French. A series of coastal towers erected in the 1780s had been criticised as being too small to provide effective firepower. Sir John Doyle, Lieutenant-Governor of Guernsey during the Napoleonic Wars, ordered the construction of three larger, improved towers being Fort Grey, Fort Saumarez and Fort Hommet. Doyle also built new military roads, one of which runs from St Peter Port to L’Erée at the northern end of Rocquaine Bay.
Fort Grey was manned during both World Wars, serving as a German anti-aircraft battery during their occupation of the island. In the post-war years, the building fell into disuse before its restoration and re-opening as a shipwreck museum in 1976. The tower has been painted white for many years as a mariner’s seamark.
It was named after General Charles, Earl Grey of Howick, K.B., the Governor of Guernsey from 1797 to 1807.
References
The visit Guernsey site has full information here.
The history above is copied from the Guernsey Museums site here.