ONLY the shadows cast by the beechwood hands on the white glass seem to be moving. The cogs, the wheels, the weights and the gears are creeping so slowly that they seem to be standing still.

But, from down below, comes a solemn click as the mechanism prepares itself, and then the bells are struck with a reverberating rumble that rocks the tower.

Another hour has passed.

It is a sound that has reminded generations of Darlington people of the passage of time for nearly 140 years and, this weekend, a handful of people have the chance to climb the 100 steep stairs from High Row to witness time in motion.

The clock tower is one of 250 buildings in the North-East taking part in the Heritage Open Days, which allow people inside the historic buildings they walk by every day.

Joseph Pease, whose family owned most of south Durham's railways and coalmines, decided the town needed a clock tower after admiring one on a continental visit. By happy coincidence, the renowned architect Alfred Waterhouse was designing a covered market - the old one, open to the smoke churned out by Mr Pease's industrial enterprises, was thought to be too grubby to be healthy - and the two projects were combined.

Mr Pease, whose statue stands at the northern end of High Row admiring his tower to the south, paid nearly £1,000 for the bells and the clock.

Work started in May 1862 and the first bells were hoisted to the top of the tower on July 21, 1864.

The Darlington Telegraph reported: "The soundness and quality of the metal was tested, the sonorous sounds quite startling the residents in the peaceful locality of the hall."

The five bells in the tower, plus two in St Cuthbert's that were, for some reason, not up to the standards Mr Pease set for his tower, are all inscribed "Cast by John Warner and Sons, London, 1863".

Mr Warner was an ironfounder in neighbouring Norton until he became a national figure in 1856 by volunteering to cast a bell for London that was so large it would become known as Big Ben.

Darlington's original clockface was red and the hands were golden. Even with gas-lighting, some of which was green so the tower was nicknamed Dracula's castle, townspeople on the street below were unable to tell the time.

So, with Mr Pease's agreement, the white face that we see today was put up.

The clock that turns the hands and rings the bells is one of only four in the country that was made by Thomas Cooke of York.

Originally, it was hand-wound three times a week, the two lead weights each requiring 70 turns on a huge handle to drag them back to the top of the tower.

Markets manager Peter Wilson said: "I took over in February 1973 from the old clockwinder, Bob Allan.

"He was an oldish chap, looked completely unfit with a big red hooter. Here was I, a young, fit bloke, and I set off at it like a bull at a gate. After 20 turns I was knackered. I had to learn all about Bob's economy of effort."

In 1977, the clock was electrified and Mr Wilson, who will be conducting tours on Sunday, laments the change. He said: "I felt like I was an integral part of the town's heritage."

Although the tours are fully booked, plenty of other fascinating pieces of the town's heritage remain to be explored this weekend.

* Read tomorrow's Northern Echo as we focus on open days in another part of the region. Find out how you can see inside a former leper house, a Second World War air raid shelter, look around the oldest purpose-built prison in England, and how you can see some Egyptian mummies