MOST of us have seen the classical facade of the mighty Box Tunnel and even sped through its two miles of darkness on a train journey, but now it is possible to take a virtual tour through this mysterious miracle of engineering.

Farmington Natural Stone, a Gloucestershire-based company specialising in Bath stone, is offering visitors to its website the chance to visit Farmington's Box Tunnel Illustrative Experience, a computer-simulated tour of the tunnel, learning interesting facts about its history and its many dark secrets, as they go.

Box Tunnel opened on June 30, 1841 and is testament to both the engineering genius of Isambard Kingdom Brunel and the hard toil of 1,500 men and 100 horses.

While digging out the tunnel a large amount of valuable Bath stone was revealed 100 feet beneath Box Hill. To take advantage of the find, Tunnel Quarry was opened adjacent to the tunnel and extensive underground stone mines were excavated.

Martin Robins, managing director of Farmington Natural Stone, said: "We decided to put this tour on our website as a tribute to Brunel, because he was responsible for enabling Bath stone to become world famous.

"We put the virtual tour up on our site on April 7, Brunel's birthday and supposedly the one day of the year when light shines down the length of the tunnel.

"As far as we're concerned, Brunel did our company a great favour by opening the tunnel.

"Before it was opened, there was no way to transport Bath stone around the country, let alone the world, but his genius changed that and as a result, Bath stone is now used internationally it was even used to build the Parliament building in Cape Town."

Connecting Bristol to London, Box Tunnel is completely straight but

deviates to a one in 100 gradient to the east.

Brunel, who was known as a workaholic, oversaw the construction of the tunnel and was even known to get down and supervise digging amongst the navvies. But his determination paid off and when the two ends of digging met, they did so with only a five-centimetre gap.

It is difficult to guess what the great 'little' man would have thought of the virtual tour.

Entered via Box Hill, web surfers find the darkness is permeated by the train track, spooky bats, discarded tools and even some of the skeletons of the 100 workers who died there.

Mr Robins said: "It's a terrific tour, very interesting and there are even sounds such as the chuff of the steam engine passing through the tunnel, the toot toot of its whistle and the rattling of the skeletons.

"We had 30,000 hits on our first day and more and more people are visiting it every day. We intend to keep it up on the site for as long as people are interested in it."

Much of Box Tunnel's mystique surrounds its role in the Second World War when the Government took over the space left by the Bath stone excavations to store its ammunition safely.

Secret command centres were also thought to be operated from the dark recesses and later the tunnel was connected to other underground facilities, including a cold war bunker called Burlington.

To take the tour log on to www.farmingtonnaturalstone.co.uk