The Gothic spires of London Bridge rise high above the waters of the Thames, but the Victorian engineering marvel that is the Tower Bridge only shows its true colors when it opens. When a ship needs to pass through, which happens up to 900 times a year, the middle splits and lifts up, an impressive sight even today. The Victorian bridge was completed in 1894, the result of a competition set up in 1876 by the Special Bridge or Subway Committee that attracted more than 50 entries. The aim was to create a river crossing that would allow traffic to cross but ships to pass into the wharfs upstream. The Tower Bridge Exhibition reveals just how this mechanical marvel works, and the final stage takes you into the impressive Victorian Engine rooms, housing the original steam engines that power the bridge lifts. (Since 1976 the bridge has been powered by oil fired engines.) A new exhibit for 2006 shows the view of the bridge opening – as if you were standing right underneath it! If time is tight, you can access the Engine Rooms only, or real engineering fans can take a behind-the-scenes tour (which must be pre-booked). For those with a head for heights, you can also wander across the top walkways, now encased in glass but with useful photo-opportunity windows. The wonderful views back up the river are well worth the climb, including the new City Hall, a bird’s eye view of the Tower of London and the impressive glass Swiss Re building, otherwise known as the Gherkin.