Ask someone what they remember about Bristol and they will probably mention the famous Clifton Suspension Bridge.

The landmark structure recently hit the headlines after one of the 162 vertical wrought iron rods cracked. The bridge shut temporarily while engineers made sure it was safe for the 11,000 commuters who use it every day.

A new rod was made and the bridge reopened last weekend.

The bridge took decades to build and the visible ingenuity around the bridge is quite inspiring. But hidden away out of site are even more marvels.

The pier on the Leigh Woods side, for example, stands on a 33-metre red sandstone abutment. For 150 years it was believed the support was solid. But amazingly, in 2002, it was discovered the abutment was actually hollow – made up of a sequence of gigantic chambers.

There are 12 chambers in all, on two levels, linked together by tiny shafts just large enough for a man to crawl through. The biggest chambers are 10 metres (35ft), almost three double-decker buses high.

The chambers have been effectively sealed since the bridge was built. No animals, bats, mice not even spiders have taken up residence, but, in several, huge stalactites up to five metres long can be found hanging in the dark silence.

Free guided tours of the bridge (on Sundays at 3pm) can tell you even more – how the bridge was conceived, built and attracts visitors from around the world.

Brunel was just 24 when he was appointed project engineer, overseeing the construction of the bridge, which had been the dream of a Bristol wine merchant almost 100 years earlier.

The merchant left a legacy to build an iron bridge over the Avon Gorge in 1754 – sceptics scoffed at the idea and said it was impossible.

The first design was produced 39 years later, but it took a major competition, held in 1829, to come up with the real possibilities, when the judge, Thomas Telford, infuriated locals by rejecting all 22 entries and declaring his own design to be the winner.

A second contest was held and young Brunel won the day, but because of a lack of funds and the violent Bristol Riots, work was held up, and he died before the work was finished by his team of engineers, and opened in 1864.

Although his work can be seen all over the country, much of Brunel's genius began in Bristol, and among his great achievements is the terminus at Temple Meads Station and the fabulous ss Great Britain – the first iron hulled steam propelled-driven ship, which has been lovingly restored to its former glory.

A temporary information point for visitors to the bridge is situated on its Leigh Woods side. About 55,000 people visit every year, to find out more about Bristol's icon.

There is plenty of material on display telling the story of the bridge – including the role of the toll keepers, 19th-century opening celebration souvenirs and historic postcards. It's open from 10am to 5pm every day and admission is free. Donations are invited as the bridge is run as a non-profit- making charity, with all the toll fees paying for maintenance work.

For more information visit the website www.clifton-suspension-bridge. org.uk or telephone Mike Rowland on 0117 974 4664.