It's a big year for Hardwick Hall, which is celebrating the 400th anniversary of the death of Bess of Hardwick. Visitors to the Hall don't need to crane their necks to see the great initials, ES, blazoned on the stonework - the faade commands att...

'From the moment you entered the Hall as Bess's guest, you'd have been almost overwhelmed by its splendour and innovation. That's just the impact she was looking for,' says Nigel Wright, Keeper of the Collections at Hardwick. The National Trust hopes visitors will get a good inkling this year of how Hardwick functioned as a family home, both for Bess and for her descendants. The last resident was Evelyn, Duchess of Devonshire, who died in 1960, and the Trust will be commemorating 50 years of ownership in 2009.

Bess moved in here in 1597 and died in 1608. She had acquired so much and was busy acquiring so much more that inventories show she still hadn't fully unpacked. Even before she had finished building the Old Hall, the ruin of which still dominates the skyline from the motorway, she was working on her grand design for a new, symmetrical building that would no longer look like a castle. Her visitors would then realise instantly that here was something remarkably different.

Over at Haddon Hall, for instance, family and servants were still eating together in the communal entrance hall, albeit at different ends of the room. Not so at the new Hardwick, says Nigel. 'The servants would still have eaten here but the family are now upstairs. As an important guest, you'd have been met at the door by a servant in livery, and whisked right upstairs. The servants would stand up and be silent and pay respect.

'The whole house is making a statement. This is a lady who had four husbands, outlived them all and managed to keep all their money.' Bess's magnificent coat of arms over the fireplace in the entrance hall proudly displays her stags, her eglantine roses, and - most important of all - her coronet. Nigel observes, 'Women didn't have their own coats of arms - they took their husband's. She'd made good and was telling them. This whole house in its position on top of the hill, the showiness of the outside, the glass, is really ostentatious. It's saying "I've got money." Outside it's the architecture: inside it's the textiles and the colour.'

Oak panelling and furniture that has become blackened over the centuries would have been honey coloured when Bess's carpenters put it in. 'As soon as you come in here, everything's lighter, to give you a lift. The tapestries would have been bright and colourful. That's how you showed off inside, with the richness of everything.' Displays on the ground floor this anniversary year will convey something of what it would have looked like when it was new - so bright that Nigel suggests, 'Today we'd have gone in and said, "Oh dear - tone it down!"'

Guests would have completely missed out the next floor and been taken right to the top of the house. Nigel confesses the gracious, curving stone staircase to have been, 'a bit of a con. It doesn't need to turn 90 degrees. When you get to here and you're looking ahead at the flight of stairs to the top of the house, you're out of breath already.' Bess created not only a sense of height but an echoing sense of space. She deliberately kept the stonework plain, white, and free of tapestries, so that when visitors reached the light box that is the top of the house, it would have felt almost like being in a cathedral.

'And then this riot of colour and scale!' Nigel says, opening the door into the Great High Chamber or Presence Chamber. The room still takes the breath away, however many times you have seen it. Quite deliberately, nothing the visitor has seen so far has prepared them for something on this scale. 'You'd have gone, "Wow!" That's what this room was meant to do, and this is where you'd have met the Countess.'

Guests eating in here - 'Never hot food, because the kitchens were too far away, and heavily spiced to disguise the fact that the meat was off' - would have been very conscious of the Royal coat of arms, a statement that Bess was loyal and had connections but also, Nigel suggests, a hedging of bets at a time when Elizabeth I was getting old and had refused to name an heir. Bess's granddaughter, Arbella, was a Stewart. '"I'm totally loyal to you, Your Majesty... and although I built this sumptuous house, I know my place.'"

The great frieze that runs around this vast room is still a thing of beauty with its sylvan groves. Scholars suggest that the depiction of Diana, goddess of hunting is another piece of flattery, a post-Armada glorification of Queen Elizabeth. In her sight-line, at the opposite end of the room, is the unicorn, the mythical creature that only the pure of heart and the virgin can see. Elephants and lions are pictured too, described by Nigel as something, 'really unusual and totally beyond the understanding of most people - to see one, you'd have been open-mouthed. The dragon supporter on the coat of arms would have been a vivid red, the lion bright gold. The whole thing would have been overpowering.'

After the meal, guests would have been ushered into Bess's withdrawing chamber, one of the private rooms. Ceilings here were lowered in the 18th century to create more servants' accommodation upstairs, so the impression of height is diminished, but this was again a room designed to impress with carved furniture which to the modern eye would have looked almost gaudy - 'You'd have been wowed just by the furnishings. Quality and colour.'

Entering the Long Gallery elicits another gasp of awe. Here Bess hung the Gideon tapestries, acquired second-hand from the bankrupted Sir Christopher Hatton of Northampton. The tapestries fit so well, absolutely level with the top of the fireplace, as to suggest she bought them before the house was built and designed the room around them.

Nigel Wright describes Bess as 'a very canny operator.' She paid well over �300 for the tapestries, an incredible amount of money at the time, but negotiated a �5 discount because they displayed the Hatton crest. 'It wasn't that she didn't have the money... Then she just got piece of woollen cloth, painted it and stitched it over the top. Hatton's symbol was a doe and hers was a stag, so she simply painted on the antlers.' In time, some of the patches have come off, revealing the original coat of arms beneath.

The tapestries are being conserved in a long-term programme which will restore the detail though not the bright colours. The walls would not have had portraits hanging on them in Bess's day but today they serve as a fascinating insight into Bess's family. Here, for instance, is Bess as a young lady, 'a fiery redhead, a whippersnapper who went to court and snared William Cavendish with her looks and charm,' Nigel says. 'He fell in love with her, she had eight children by him and he doted on her. She was able to persuade him to sell all his land in the south of England and buy land in Derbyshire! From their letters, it appears to have been a happy marriage.'

The sweet-smelling rush matting in the Long Gallery and elsewhere in the house looks much as it would have looked in Bess's time. Made from rushes harvested in Cambridgeshire, it is cut down very traditionally, dried and woven, and has to be kept watered to keep it supple. 'Carpets were for hanging: you certainly wouldn't have walked on them,' Nigel observes. The enormous state canopy in this room is a wonderful example of thrift: originally a bed at Chatsworth, it was passed on to Hardwick second-hand when Chatsworth was remodelled in 1697.

It's when the visitor gets to the bedroom with its gargantuan stone fireplace that the domestic arrangements become interesting. 'People tend to think this must have been Bess's bedroom because it is the best. But you are on the top floor, the show floor,' Nigel points out. 'A house like this always has draughts, and most of the time, this would have been too cold, only warmed up for special guests.' The Sixth Duke called it in his notebook, 'that wilderness of a room with a Derbyshire quarry in the corner.'

Although Mary Queen of Scots was not imprisoned at Hardwick, it fell to Bess's fourth husband, the Earl of Shrewsbury, to pay for what was closer to house arrest in the various places to which she was consigned. 'The marriage breakdown wasn't helped by the fact he had to look after Mary, who was actually executed three years before Hardwick started. The poor guy had two women spending his money and Bess was also spending money at Chatsworth like there was no tomorrow,' Nigel says.

The Trust has exploited the Hardwick connection to give the visitor a glimpse of the life of Mary, a much romanticised figure in the 19th century. Some of the furniture on display in the bedroom that is The Mary Queen of Scots Room might well have come from Mary's apartment at Chatsworth, and the Cavendish family certainly promulgated her story over the centuries, Nigel suggests. He points out, 'A house like this would have been a tourist attraction in its own right. If you'd have come and knocked on the door and given the housekeeper a few shillings, she'd have shown you round.'

Walking down the wooden stairway to the middle floor feels very much like using the back stairs. The scale of everything reduces immediately to become almost domestic, because this is where the family have actually lived over the years. Bedrooms have become suites of rooms with dressing rooms and bathrooms. 'One begins to lose a bit of influence - this has been lived in more,' Nigel says, as we move into a dining-room very different in scale from the High Great Chamber.

This room and the sitting room are laid out very much as they were when Duchess Evelyn lived here, and are almost homely. The connection with Bess remains in tapestries she bought from the same source, with the same rough patching over the Hatton coat of arms, but the scale and character of the rooms has changed dramatically. Bess's bedchamber is on this floor and will be open to the public this year. It is a small and modest room with windows facing south and west, chosen for its sunny aspect and its warmth in winter. The carvings by the fireplace, which she chose, are almost crude in their simplicity and are nothing like the elaborate carvings on the show floor.

Temporary exhibitions this year will tell the fascinating story of how the house developed as a home. On a behind the scenes tour, the picture is complete when you finally come face to face with the Fifties. Fragments of floral wallpaper. Chilly bathroom. And an orange Formica floor.