I was just in Waterloo station, one of London's great train hubs interconnecting the Underground, British rail lines and Eurostar, the train that flashes through the Chunnel into France. As with any station in London, people were striding at full pace in every direction - lights, signs, newsstands, bars and shops, all in full surround, yet mostly what you heard was thousands of tramping feet in a cacophony of cadences.

Shops of modular construction dot the vast main floor, so it's possible to catch a respite by simply stepping between two. This was exactly what one harried businessman did. His tie loosened, his suit jacket open, his head buried in his forearm, leaning against a wall, heaving great breaths, face red, heart obviously pounding, holding tight onto the briefcase in his other hand.

It was easy to surmise he had raced up the stairs from an underground train, forcing himself to keep pace with his fellow commuters. Whatever the story, he looked to be a typical man in his forties, somewhat thick about the waist, but still with a great chunk of life ahead of him.

If he lived that is. If you're not in good shape, the Underground can kill you.

That bit about "killing you" is really just a figure of speech, although you should try it some time. The first tunnels of the London Underground were dug 150 years ago, in what was called the "cut and cover" method. These are the routes closest to the surface, but as London grew and construction technology evolved, layers of criss-crossing train tunnels could be dug out, deeper and deeper.

That familiar map of the Underground, on everything from coffee mugs to tea towels, shows each route in a different color, its stations tickling your brain: Charing Cross and Piccadilly Circus, High Street Kensington and Tower Bridge, Paddington and Victoria. It's there on every car on every train, and if you see one in situ, the odds are you've just maneuvered yourself down more stairs than you can remember descending in recent memory, and you did it at "Underground pace."

No lolling about here. Everyone is on their way to someplace else.

As a newbie, I relied anxiously on these maps, staying on high alert to find my station, where I would then leap off, face the stairs and walking tunnels, and switch to another line.

At one point, I realized a few stations were marked with the universal symbol of a person in a wheelchair. It meant you had full access using lifts, and I already knew this doesn't mean that the rest of the time you get to take the escalator. We Americans have forgotten what life was like before the Americans with Disabilities Act. There is simply nothing like this anywhere in the US - up, down, over, a maze of climbing, turning and continually making sure you know where you are going. There is no telling how far you have to walk, how many stairs you have to climb, and what kind of "gap" you may expect when the train arrives. "Mind the gap" is the ubiquitous sign meant to remind you that there is a space between train and platform, and there may even be a step up or down.

It's then I noticed the riders were mostly under 50, and strollers and rolling bags were few and far between - difficult equipment to be toting at breakneck speeds.

One hundred and fifty years ago, it was a miracle that they could even build an underground. And to be fair, retrofit on the oldest parts of the London Underground would be wildly expensive. Still, it's at times like this I am reminded that the ADA benefits us all.

I'm Moira Gunn. This is Five Minutes.