What do suspiciously shaped "relaxation aids" for Victorian ladies, a priceless collection of handwritten notes by John Clare and a chair belonging to a 53 stone man have in common?

The answer is that they can all be found deep in the darkest vaults of Peterborough Museum.

And they are likely to stay there, at least for the near future, as for every one item the museum has out for the viewing public to see, there are seven neatly stored in the back basement.

But The ET was granted special access to the Priestgate museum's hidden gems – as you could be: all you have to do is ring up and ask, and the kind folk at the museum will be happy to accommodate you.

Collections and interpretation officer Sarah Wilson said several people from across the country have turned up at the museum to see its Turner painting – JMW Turner is considered one of the finest artists who ever lived, and the prestigious Turner Prize for art is named after him.

"It would be a shame to turn them away," said Sarah. "And so we let them have a look. We are very, very lucky to have a Turner – a small painting of Peterborough Cathedral, done very early in his career.

"It's difficult to put a price on things like this, or anything we've got, because a lot of the time you don't know what something is worth until you sell it – and even then it can go for a lot more than the asking price."

The vault isn't as deep and dark as you might expect – it can't be, as Sarah and other members of staff spend much of their working day down there, making sure all is well with the collection.

"A big part of my job is making sure that no rats or mice get in here," said Sarah. "We wouldn't want our Turner or our John Clare notebooks nibbled!"

One recent visitor to the vault was the Lord Lieutenant of Cambridgeshire, who was fascinated by the art collection. "He had met the painter Mary Fedden, and wanted to see some of her work which we hold here.

"He spent a long time looking through the collection, and was really impressed. He said we were very lucky as a regional museum to have so many interesting things, and we really are."

Mary Fedden is one of the UK's best-loved contemporary painters, and her work sits in the vault alongside Crow, a picture by Dame Elisabeth Frink, who is one of our leading sculptors, and another by Walter Sickert, a very well-respected Victorian painter who is thought by some to have been the real Jack the Ripper.

But the artworks aren't the only interesting pieces to be found in the back basement – there are lots of archaeological treasures, plus an extensive collection of military history.

"It makes us laugh sometimes because in the past, curators were men. They didn't always care too much for ladies' costumes and hats, but really loved all things military, and that came across in the things they collected," said Sarah.

One of the more intriguing military items is a Christmas Tin dating back to the Boer War, which Queen Victoria sent out to her troops between 1899 and 1902.

The boxes would have contained chocolate and cigarettes, and although someone has puffed the cigs into the ether, the chocolate has survived – but doesn't look very tasty.

The museum is regularly given new goodies by generous donators, usually when someone dies and their family thinks something might be of interest. "We have had a lot of sewing machines," said Sarah. "And Hoovers. But the most interesting thing given to us recently was in summer last year – we were given a doll's house."

And this wasn't any old doll's house – this was a doll's house made in the 1850s by the father of the Brewster family for his children. The Brewsters used to live at the Old Still, which is now part of Queensgate.

"Four or so generations played with the house, which came with all the furniture, and they decided to give it to the museum as it was getting a bit old, and they thought local people would enjoy seeing it, and they did when it was in our Christmas exhibition this year.

"When people give us things it is always more interesting if they have a little story to go with it, it really makes the things we have come alive.

"For example, someone recently gave us a parcel a soldier sent to his family in the Second World War, and they knew all about it, all the little stories, and what they told us was one family's experience of war. Local, personal stories like those should be what a museum such as Peterborough's is all about."

Lots of us often drive or walk past the museum, but don't stop by. But perhaps we should. Exhibitions change all the time, things come out of storage . . . from a painting by Jack the Ripper to some fossilised chocolate, you never know what you're going to find.