Set against tall cedar trees, Highclere Castle looks majestic. My heart jumps with excitement much like a pilgrim's on seeing a place of worship.

Like millions around the world, I have become a fan of Downton Abbey and devour every single episode gluttonously. For the last five years, it has become a ritual for me to snuggle into a favourite chair with a hot cup of tea and spend cold Sunday nights from September to Christmas in the company of Lord and Lady Grantham, their daughters, Mary, Edith and the late Sibal, their grandchildren, extended family and large retinue of servants.

We laugh at the wonderfully-written, cryptic one liners allotted to the Dowager, delivered superbly by Dame Maggie Smith, cry with Mrs Crawley (Penelope Wilton) on the death of her only son Mathew and rejoice with the Lord's valet, Bates, and lady's maid Anna as they finally overcome obstacles to their marriage. Their home "Downton" is such an integral part of the series that it has virtually acquired the status of another cast member.

Highclere Castle, which doubles up as Downton, is set in 1,000 acres of sweeping parklands in the English county of Berkshire, about 100km north of London. While it is said to have been built around 900 years ago, the old brick and freestone house was converted into a classical Georgian mansion in the late 18th and early 19th centuries.

Today it is the home of the 8th Earl and Countess of Carnarvon, who for a brief period during the summer months open their home to public viewing like many other stately homes in the United Kingdom.

Downton Abbey has become a real money-spinner for Highclere Castle with visitors' footfall tripling since the series began, so much so that tickets (at £20, or about Rs 2,000 per person) have to be booked online and the slots are fully booked long before the summer season begins.

The large wooden main door of Highclere Castle opens into an arched porch leading into the heart of the house. The saloon, as it is called, is where parties are held, guests are received and secrets overheard. Built in a Gothic style with arches on all four sides of the rectangle, and a ceiling going well above two floors, the masterful stonework has detailed carving with the crests of the Carnarvon family a recurring theme.

The wall coverings, made of leather, were brought back from Spain by the 3rd Earl. As I stand next to the at least 8-foot-high fireplace I can see Hugh Bonneville as Lord Grantham giving his Christmas eve speech at "the servant's ball".

All the furniture seen in Downton actually belong to Highclere. "The crew simply move in with their equipment and the cast with their costumes. No props are needed," says a guide. "We just remove all the family photographs and personal effects that don't belong to that period."

On public view on the ground floor are the state rooms which include the saloon, dining room, library, drawing room and smoking room.

"The dining room is much smaller than it looks on TV. This table only seats 10. I guess bigger tables must be brought in to accommodate all the guests at the large dinner parties that Lady Grantham regularly throws," says a woman in an American twang. The series has been a huge success in the United States, dominating the Emmy awards. Fans visiting Britain make a point of coming to Highclere to pay homage.

We file past the red sofas in the library with the furniture cordoned off on both sides, not to be touched. The walls hold over 5,650 books. The desk at which Downton fans see Lord Grantham deal with the affairs of his estate was used by the 4th Earl of Carnarvon to write letters as a member of Conservative Prime Minister Disraeli's Cabinet in the 1860s.

The drawing room, where the Downton family usually retires to after dinner for drinks, discussions and drama, is decorated more opulently. The walls are covered in green French silk gifted in 1895 by Alfred de Rothschild to his illegitimate daughter Almina, who was married to the 5th Earl of Carnarvon and given a stupendous dowry.

In 1914, when World War I broke out, Almina turned Highclere Castle into a working hospital and admitted patients coming back from the trenches. She herself headed the nursing staff. Writer Julien Fellowes borrowed this piece of real history when he turned Downton Abbey into a convalescent home for wounded soldiers returning from war.

Cashing in on the popularity of the TV serial, Fiona, the present Lady Carnarvon, wrote her first book a couple of years ago based on the life of Almina. After the success of Lady Almina and the Real Downton Abbey, Fiona followed it up with a second book called Lady Catherine and the Real Downton Abbey, which charts the life of an American girl who married Lord Porchester, the son of the 5th Earl of Carnarvon. At just 19, Catherine had to learn to organise and host lavish banquets and weekend house parties and manage the more than 80 staff working at Highclere Castle. Considering the similarities with the fictional Lady Grantham, perhaps Fellowes pinched the character from Highclere's real history, too.

The intricately carved oak staircase at one side of the saloon leads up to the 11 bedrooms on the first floor, but not all are on public view. Some of the bedrooms are marked with names of the Downton family. Visitors are not allowed to enter but peer in at the open door. Highclere has another 40 or 50 bedrooms on the other floors but they are no longer in use, nor open to the public.

A stone staircase behind the green baize door leading from the saloon winds down to what were the old staff dining rooms, cellars, sitting rooms, utility areas and kitchens. The Downton sets department recreated these at its studios in London and all the "downstairs" scenes are filmed there.

Also on display at Highclere is the 5th Earl's Egyptian collection. The earl, along with his archaeological colleague Howard Carter, discovered the famous tomb of the Egyptian boy pharaoh Tutankhamun in 1922. The themed exhibition of the discovery of Tutankhamun's tomb includes over 60 replicas, wall paintings of the tomb and photographic archive. Following his death in 1923 the collection was sold by his widow to the Metropolitan Museum of Art in New York to pay hefty death duties.

Carter had commented that he had left a few unimportant items at Highclere. These were all tucked away in cupboards until re-discovered by the family in 1987 and now exhibited.

The final series of Downton is being aired in the UK. Fans have braced themselves to say goodbye to their favourite characters in a couple of months, but there are already rumours of a film.

The success of Downton not only gave the opportunity to many British actors to showcase their talent, but it also brought a very fine English mansion to the notice of the world.