As well as iconic contents like the giant Blackburn Beverley aircraft, there is a human skeleton - and a rather gruesome Royal relic .
Some years ago the owner of Paull Fort bought a macabre salt cellar from a museum in York - allegedly made from a vertebra taken from the coffin of King Charles 1, who was beheaded on 30 January 1649.
It is said to have come into the possession of Sir Henry Halford, who was a physician to various members of the Royal family, when the body of the sovereign was discovered by accident during building work in St George's Chapel in 1813.
The circlet of bone, which had been converted into a salt cellar, with a gilt stand and a small mother of pearl spoon, was displayed at the Fort and at the Royal Armouries in Leeds in an exhibition 20 years ago marking the 350th anniversary of the monarch's execution.
The Blackburn Beverley XB259 was moved successfully to Fort Paull in 2005 from its old home outside the Museum of Army Transport, in Beverley.
The plane, which was originally built at Brough, near Hull, is the only one of its kind left in the country.
Its last ever landing came on March 30, 1974, at nearby Paull Airfield. The plane never saw squadron service with the RAF, but was used for tests and modifications.
Moving it again will prove a major task - when it arrived at Paull Fort a large crane was used to lift the large parts of the airframe over the fort’s walls.
Another aircraft owned by the Fort is the Hawker Hunter XF509 which started out with 54 Squadron in 1957 and came to Hull in 2005 where it was fixed on a pole outside the former Humbrol factory on Hedon Road, once famous for making Airfix model kits.
Auctioneer Andrew Baitson said they felt "honoured and privileged" that the owner had asked them to auction the fortress.
They would look to sell it and its contents in its entirety, but should there be no acceptable offer then they were looking to hold an auction in June. In all there could be 1,000 lots.
He said: "There are a few items that belong to third parties, and we will get those collected by the owners. Anything left we will sell.
"This has taken 30 years to put together - it is difficult to put a price on it.
"There's a lovely Henry VIII display, and of the Crown Jewels, and the Napoleonic Wars display, and of the World Wars.
"There's all the waxwork models of the Royal family, Churchill, Hitler, Henry VIII, Ann Boleyn, all the artillery, anti aircraft guns, Russian and other tank turrets and armoured personnel carriers.
"It's going to be a very big job and it's going to take some working out.
"At the end of the day who else has sold a collection like this before. It is a one off it really is."
He said he believed the fort, which has a mile and a half of walls, could make a great activity centre.
"It has a great deal of potential for someone to take it on, whether it is another War Museum, whether Eden Camp would be interested."
Mr Baitson said they needed to look at the legislation involving the sale of human remains.
"We have never sold a human skeleton before, not a real one."
He added: "The Blackburn Beverley is going to be tricky, with the logistics alone in moving it."
Last time it was moved the plane's wings - some 180ft across and weighing 12 tonnes - had to be taken off before being refitted.