London’s 272-foot, dual-bascule bridge began as an architectural conundrum. As the East End of the capital city became more densely populated in the 19th century, the city needed a new crossing structure downstream of the London Bridge, but could not afford to disrupt river traffic in the process. The solution? A bridge that could raise and lower to allow river traffic to pass. It took more than 50 design submissions, eight years, five major contractors and 432 construction workers, but by 1894 the Tower Bridge was finally completed. The finished product was an architectural marvel—at the time the largest and most sophisticated bascule bridge ever built, which powered its 1,100-ton decks with steam hydraulics. Impressive engineering by day, yes, but the bridge is even more spectacular at night, aglow with floodlights illuminating its fairy-tale turrets. Tower Bridge Rd.; 44-20/7403-3761; towerbridge.org.uk.