Haile Sand Fort

Following the outbreak of the First World War, English towns and cities like Hull, Grimsby and Immingham came under aerial attack, first from German airships, then aeroplanes.

Work started on building two forts on the mouth of the Humber Estuary in 1915. This one is off Humberston, Lincolnshire and Bull Sand Fort lies off Spurn on the Yorkshire side, seen in the distance below.

Soldiers were billeted in Cleethorpes (4000 by 1916), including at the Fitties camp which continues today as a chalet park. Up to 200 soldiers could stay on the fort itself.

It opened in 1917 and construction wasn't fully complete until 1918. It stands 59ft above the water ane has a diameter of 82ft.

Costing up to half a million pounds, according to Cleethorpes Heritage, no shot in anger was fired. Indeed, Bull Fort was so hard to build, built on sand 120ft down that it was only completed a month before the end of the war.

The effort was not wasted though as they were reactivated and modernised in WW2, seeing much action. They hosted "12pdr QFs and then 1940 with twin 6-pounders" (Victorian Forts). Netting was laid across the estuary to stop submarines entering.

Abandoned in 1956, both forts survive the sea's onslaught. Bull was bought by a charitable trust in 1997 for £21,000, with unrealised plans for a drug rehabilitation facility, while this one's on the market.

Accessing the fort

It sits a good mile from shore at high tide, and around 100 yards at low tide.

The tidal distance is huge here and when venturing from dry land, attention needs to be paid to the channel separating the vast high sands beyond. It's a 15 minute march to the lower-tide shore.

Wind and current affect conditions. An outgoing tide is beneficial for reaching it, but potentially unforgiving if turning around and swimming against it.

Around 100 years of being pounded by saltwater has made the ladders and wooden jetty treacherous, ready to collapse at the slightest tug. Rusted metal under the surface is an elaborate spike pit. Near the low tide mark: sea mushrooms—big, white bulbous growths attached to the edges.

Beams covered with barnacles and seaweed offer access to the platform.

The panels are weather scarred, rusty and colourful. Doors are sealed. There's no easy way of climbing up to the windows above. You're cold, with numb hands and feet. Your chest and stomach get cut climbing down. You swim back.