Behind the Scenes: Engineering tours at Tower Bridge The tour begins on the raised walkways, with their crowd-pulling views over the rapidly ascending Shard and the skyscrapers of Canary Wharf. From these chilly, glass-encased platforms, our guide talks us through the celebrated construction innovations behind the Gothic marvel, known to the Victorians as the "Wonder Bridge," and recounts key moments in its past that have since become legend. The mechanisms of the lift itself become (slightly) clearer once the tour leaves the attraction's common areas and descends to the engine room, where the handsome original Victorian motor is still in place beside newer machinery. Charles Lotter, one of the bridge's senior technical officers, explains to us how it draws back the bolts that hold the two bascules together and sets the counterweights in motion to draw the two parts upwards. This process occurs around 1,000 times a year; any vessel can request a lift provided they do so in advance, in writing, and are not late for their appointment. The staggering feat of engineering that became the toast of Victorian London still attracts tourists every time it takes place (lift times are published daily on the website). The bascule chamber of Tower Bridge From the engine room we are led down a very steep and narrow spiral staircase to the bottom of one of the cavernous bascule chambers, under the bridge. This is where the counterweight swings down and fills as the bridge above ascends. It is an impressive, and rather unnerving, experience to stand at the foot of a giant chamber built into the river itself, not least a freezing, dimly lit one. Charles, who has inexhaustible knowledge about all components of the bridge's functionality, explains that an infrared braking system halts the descent of the counterweight. There was a subtle schism in the group at this point, however: those with an engineering background were enthralled by the level of detail and used the opportunity to ask as many specialist questions about Victorian construction methods as possible; those of us without a similar level of expertise became quickly conscious of the cold and lost in the minutiae being discussed. Inside the Tower Bridge engine rooms. Image: Tower Bridge After the group's questions are depleted, tours return to ground level and end in the public engine room to see the retired steam pumping engine and boilers that powered the bridge since it opened in 1894. The tour offers a highly informative lesson in the bridge's unique dynamics and functions, as well as showing off its historical legacy. Engineering enthusiasts will be fascinated by the guides" boundless knowledge of bridge mechanics, but, for novices, such detailed immersion in technical terminology may not be quite as appealing. Whichever camp you fall into, be sure to wrap up warm. Tours run every Saturday and Sunday until Saturday March 31. The tour costs £30 per person, including a Tower Bridge guidebook, and must be booked in advance; call 02074079191 to register for tickets or visit www.towerbridge.org.uk for any further information