Fort Darnet was built on the recommendations of the 1859 Royal Commission, on an island covering the inner navigable channel of the River Medway, Kent.

Originally designed for two tiers of guns mounted in a circle, with a boom strung between them, there were many problems with subsidence, and after extensive cost overruns the forts were completed in 1871 with one tier, 11 guns - a mixture of 9-inch and 7-inch rifled muzzle-loaders - and no boom. The forts were never used in anger, and were disarmed before the First World War.

In the Second World War the fort was used as observation posts, with platforms and pillboxes built on top. The fort is still in fair condition, though the magazine level is flooded.

Depending on launch location there will be a boat trip that is unlikely to be less than about a 5 mile round trip, on tidal waters. I have visited half a dozen times, launching either from Sharp's Green Bay, with very convenient parking at N51 23.209 E000 35.635, or the Strand at N51 23.789 E000 33.787, where you can park along the access road after unloading your equipment. At Sharp's Green Bay in particular do not miss the tide window - other than around an hour each side of high tide you will have difficulty with deep mud. The Strand involves a longer voyage but there is a little more shingle and sand, and a small causeway, which together open up a slightly larger window.

When you reach the island, approach from the west - there is an appropriate beach behind the sunken barges which act as breakwaters. From the landing beach there is a track through the undergrowth to a 9 inch wide, 10 foot long gangplank over the moat.

The island on which the fort is built is part of the Medway Marshes SSSI. The purpose of the designation is to protect the habitats of sea birds who breed on the mud flats. The fort is built away from the mud flats themselves, and the route described above avoids them. Take particular care to avoid disturbing them during the breeding season from beginning of March to end of July.

There is also a Groundspeak cache on the island.