Mind the gap: Walking London's mysterious drawbridge, Tower Bridge

Massive, with Draconian stone towers hulking over the Thames, London's Tower Bridge appears as a fortress daring anyone to attack. In fact, what seems to be solid, old stone is actually mere facing disguising a monstrous core of steel--one so dense that doubters thought such a bridge couldn't possibly stand. And Tower Bridge is, as I learned on a fantastic tour (five pounds fifty; about $10), riddled with secrets.

The dun "stone," with its upper and lower walkway and elfishly small, wooden doors unexpectedly peering out of the bridge walls, has always looked medieval to me. In fact, the original design was conceived to please decision-makers who were righteously opposed to any modern- or industrial-looking blot on the Tower of London's riverscape. A new bridge, especially one this large, needed to appear natural if it hoped to be approved by the elders in charge. So in the 1880s, architect Sir Horace Jones drew up an incredible facsimile of old England, but with modern gears and a steam engine inside.

While I'm sure that all the tower's guides are excellent, I recommend the one who led my tour: a blue-eyed, soft-spoken gentleman named Geoff Wooltorton. Every step he took across the upper walkway--a glassed-in span with several small sets of steps for elevated viewing--Geoff had a story to make us tour-goers gasp or laugh with the amazed sense of knowing something new, a secret of the bridge.

The first whisper: It's because of Tower Bridge road rage that the English now drive on the left. "In those days [the late 1800s]," said Geoff, "people had horse-drawn carts. They'd hold the whip in their left hand and the reins in their right. They'd drive in the center of the road, and use their left hands to whip any passing driver who annoyed them." So a law was passed: Drive only on the left. That way, the whipping hand would be aligned with the wall, not with another driver.

Then there's the creepy spot called Dead Man's Hole, at the base of the bridge. "Don't ever let anyone tell you that was named for suicides," announced Geoff. "Tower Bridge was never a favorite spot for  uicides." The truth: "That area was part of a slum. When anyone died there, their family couldn't afford burial. So any bodies would be slid into the water at night, from that spot."

And there's the hidden party spot at the bridge. To find it, look to one of the small, wooden doors along the bridge. This is the bridge master's flat. Those in the know have weddings performed inside--that is, inside the bridge, itself. The reception (or any other type of party) can be held on the twin upper walkways (they run almost side by side across the bridge, both glassed in and warm): one will hold the buffet; the other, a band and space for dancing (as close to "on air" as one can imagine, with a  panoramic view of London and the water far below).

While only partially obscured from view, downstairs is the not-to-be-missed old engine room. Originally, the two 1200-ton arms of the bridge rose on steam power, but today, the two coal ovens that heated it are unused and sparklingly restored (the bridge is now automated). The enormous turbine wheels, all painted avocado green with black and red pinstriping, make impressively huge revolutions against the backdrop of a turning metal egg that resembles something from Edison's laboratory or Da Vinci's sketches. It
is gaspworthy.

Finally, the secret to scheduling a great viewing: Check online. The bridge closes several times a day for scheduled drawbridge lifts, which are truly impressive with tall ships passing beneath. They are less impressive for drivers. One day in 1950, a double-decker found itself leaping, Speed-style, over a three-foot gap created when the bridge rose...with the bus still on it. So while you're discovering the many hidden charms of the bridge...just be sure to mind the gap.