Sun and rain ravage Bess's proud pile

"One of the proudest piles I ever beheld," wrote John Byng, Lord Torrington, of Hardwick Hall in Derbyshire. "Pile" is a mite derogatory for one of the finest Elizabethan mansions in England - perhaps the word had a gentler meaning in 1798 - but Hardwick is a monument to pride.

Elizabeth, Countess of Shrewsbury, better known as "Bess of Hardwick", was the local squire's daughter made good. The hall she had built in the later years of her long life was designed to impress

This year the National Trust is celebrating Hardwick's 400th anniversary. Bess moved in on 4 October 1597 to accompaniment of music played by four servants. The decorators were still at work for another three years - but what the visitor sees is substantially as they left it.

Well, not quite. As Simon Murray, the trust's historic buildings representative, has put it: "Today Hardwick looks like a petrified butterfly; the form is the same, but all the colour has gone, bleached away by the light streaming through those enormous windows."

Rain water streams in too, collecting in pools on landings and the gallery floor. The trust estimates that pounds 18m needs to be spent over the next 10 years, mainly on stonework and saving Bess's tapestries and embroideries from disintegration. The textiles are unrivalled in Europe: the hangings have remained "at home" for 400 years.

The trust is applying to the Heritage Lottery Fund for money to carry out essential conservation work on three major properties - Knole in Kent, appropriated by Henry VIII, Petworth, West Sussex, and Hardwick. In total, pounds 40m worth of work needs to be done.

Bess's initials ES stand in bold stone silhouette beneath a coronet on every turret. Long, diamond-leaded windows underline her wealth. "Hardwick Hall, more glass than wall," ran a contemporary jingle.

Hardwick rises from a hill top above the M1 just south of the exit for Chesterfield. But only its close relative, Chatsworth House, is signposted from the motorway.

Bess was driven out of Chatsworth by the Earl of Shrewsbury after their marriage ended bitterly, the pair intriguing against each other at Queen Elizabeth's court. And although Chatsworth remains the property most closely associated with Bess's descendants, the dukes of Devonshire, Evelyn, widow of the 9th duke, remained a tenant at Hardwick after the trust took over in 1956.

Thirteen tapestries, telling the story of Gideon and his triumph over the Midianites, run the full 162 feet of the Gallery.Daylight and sheer weight have seriously degraded them. The cost of repairs is put at pounds 1.5m.

The trust has never shouted about Hardwick. It is a fragile place and the 70,000 visitors the hall receives each year were reckoned about as many as it could bear.

Turning on the spotlight in support of the lottery bid will probably increase the numbers, but curator Gill White thinks Hardwick can take the strain of another 10,000 admirers.