Deep in County Durham, overlooking the undulating hills of Cumbria and North Yorkshire, sits a large and imposing French chateau.

With its pale, golden stone and deep lead roof, it looks as if it has been lifted by a giant hand from the Tuileries in Paris and set down in an alien landscape.

It is the result of a love story and a passion for collecting that bordered on obsession.

The man who gave his name to the treasure house within the distinctively French exterior was John Bowes, a wealthy Durham landowner, horse breeder and coal magnate who never threw off the taint of his illegitimacy.

In 1848, he moved to Paris, where he bought a theatre and met the woman who was to be the love of his life, an actress named Josephine Chevalier. Perhaps it is just as well Bowes rescued her from treading the boards, as one waspish critic said of her that she had "an impossible voice, impossible figure and . . . sings down her nose".

She shared Bowes' love of fine art and collecting; together they dreamt up the idea of creating a museum at Barnard Castle in his native Teesdale. And that is what makes the place so unusual.

It's not a former stately home that has been adapted to display the possessions of an aristocratic family no longer able to afford the inheritance tax. It was purpose-built to house a collection amassed with one idea in mind: to create a place where local people could come to marvel at some of the world's finest treasures. And, as collections go, it's a whopper, bought almost entirely in a frenzied shopping spree lasting 12 years. The Boweses amassed items at a rate of just over 1000 a year - paintings by artists including Corot, Boucher, Goya and Canaletto as well as sculpture, miniatures, prints, ceramics, glass, metalwork, furniture, clocks and watches, automata, objets d'art, tapestries, embroideries, clothes, Roman antiquities, geological specimens, architectural woodwork, books and manuscripts.

One of the best-known exhibits and one of the most expensive purchases is a musical automaton in the shape of an exquisitely crafted silver swan, made in 1773 by John Joseph Merlin. The Boweses almost certainly marvelled at it at the International Exhibition in Paris in 1867, where it caused something of a sensation.

Mark Twain described watching "the Silver Swan, which had a living grace about his movements and a living intelligence in his eyes ... swimming about as comfortably and as unconcernedly as if he had been born in a morass instead of a jeweller's shop - I watched him seize a silver fish from under the water and hold up his head and go through all the customary and elaborate motions of swallowing it."

The life-size swan is in action at the museum every day at 2pm.

On a less grand scale, but equally intriguing, is a gold mechanical mouse bought by Josephine Bowes in 1871. Decorated with seed pearls, with garnets for eyes, the mouse scuttles along, stops, changes direction and scuttles on again.

There is an eclectic and personal nature to the collection that makes it fun. Alongside the tapestries (one of the largest and finest collections in Britain), the paintings by El Greco, Fantin Latour and van Dyck, and the fine and plentiful ceramics, there are a pair of socks from Persia, a sugar basin from Turkey, two wooden spoons from Romania and a Georgian cabinet so specialised that no one is quite sure how it really works. If you open its side door, there are numerous trays that once thrillingly kept botanical specimens from expeditions to the Cape of Good Hope in the 1770s.

This mysterious and ingenious little cabinet has its own plumbing, with lead water pipes that run up the legs and a set of taps.

As the Boweses began constructing the building , disaster struck. Josephine fell ill, and by the time the foundation stone was laid she was too frail to do anything other than touch it with a silver trowel.

She died young in 1874 and her husband's passion for collecting died with her.

By the time their magnificent endeavour was completed and the Bowes museum opened its doors in 1892, John Bowes was dead, too.

Neither had lived long enough to see their dream become reality.

As more than 60,000 people turned up at the museum's grand opening, the Newcastle Chronicle wrote: "The Bowes Museum is an institution which will probably do more in future years to bring fame and fortune to that quaint town than all its other attractions put together."

How right it was.

The Bowes Museum, Barnard Castle, Co Durham opens daily 10am-5pm. See thebowesmuseum.org.uk. A show of more than 60 David Hockney prints will be held at the museum from June 7 to September 28.