"What's wrong?" I asked.

"We missed our last train by just one minute!" moaned one of the women, an office worker who said her name was Kumi Kaneda. "The cab home's going to set me back 8,000 yen."

"It's our fault. We walked too slowly," acknowledged her taller coworker, Noriko Tamahiro.

"We're drunk," confessed Kaneda.

"Even so," I said, "do you think it's right for the trains to stop so early?"

Tamahiro weighed in. "The government nags us to clean up the environment, but it's because of this transportation system that people drive cars as much as they do."

After a moment's pause and with a bat of her eyelashes, though, Tamahiro noted that the status quo may have at least one benefit.

"When the trains stop running," she said softly, "boys and girls spend the night together."

An interesting point, and one perhaps worthy of further discussion. But as the women started rubbing their arms from the cold, I bid them farewell and went on my way.

Further west, across the street from the Imperial Palace, I came upon some guys in hardhats milling around a construction site. Approaching one of them, I explained my mission. "Follow me," he said with a genial smile, and waved me through a barrier and into a hut.

From there, I was surprised to find a staircase descending into a cylindrical hole deep enough to fit a large locomotive. Shouting over the deafening racket of a cement mixer, my guide, civil engineer Hiroshi Kotakemori, explained that the shaft would soon house part of a "central artery," which will include sewage pipes, power and communication cables. Nearby, he said, was an even larger subterranean site the size of "four tennis courts."

Far below the landing, workers bustled around this stygian domain, nocturnal denizens of a hidden world attending to an intricate network of pipes protruding from the floor. Many of these men, I learned, spend half the year working at night.

Emerging from the hole, I ran into 69-year-old Sukio Hazaki, one of the countless "traffic coordinators" who wave illuminated red batons on the streets and sidewalks around Japan's construction sites. If anyone was emblematic of Tokyo's streets at night, it was Hazaki. I asked if I could photograph him at work.

"Well, I don't know. Not many cars out right now," he said, peering down Sakurada-dori. But a taxi eventually rolled by and I snapped away.

Although there was little traffic for Hazaki to coordinate, he felt no lack of mission, as he was also charged with keeping suspicious characters away from the area's many important buildings. "Getting to work this close to the Imperial Palace sure is swell!" he gushed.

"But what does your wife think about your late hours?" I asked.

"She prefers I'd work days," he said. "But she knows this is better than my staying at home and going muddle-headed."

With that I bade farewell to Hazaki and the hardhat crew and continued west past the ranks of drab Kasumigaseki offices where, by day, armies of bureaucrats busily operate the gears and levers of officialdom.

As I walked in a light rain, with the sidewalk all to myself, the mood had slowed to a blissful calm. Lines of taxis girdled the ministries and agencies, their roof lamps twinkling fireflylike in the slim hope of attracting fares. I imagined being inside a colossal Christmas tree.

Walking on in this pleasant reverie, I soon found myself at a corner in Akasaka occupied by an attractive, smiling woman.

"Massage?" she asked. Behind her, women in mini-skirts deposited their drunken male clients into limousines.

I thought about the woman's entreaty. I had often heard it said that there was more to be had at these so-called massage parlors than a mere massage. But I'd never found out for myself. So, in a spirit of professional research, I followed her into the elevator of one of the street's many nondescript tall, narrow buildings.

As we ascended, she informed me that she was Taiwanese. "I like Japan, but not the Japanese," she said, without elaborating.

In a fifth-floor room with green wallpaper, she presented me with a glossy, restaurant-style menu of "courses." A no-frills massage, she said, went for 6,000 yen. But "special services" could push the bill up to 20,000 yen. Describing in detail the extra offerings -- each more lubricious than the last -- she never flinched from her businesslike manner. Certainly, after her menu run-down, I can vouch that massage is only a fraction of the goings-on at such establishments.

I gently declined. She came back with a 40 percent discount. I held my ground. When she persisted, I came clean, admitting I was a reporter researching for an article, and we went back outside.

"You can think about your story while I give you a massage!" she said, not giving up easily, and offered to settle for the "preferred-customer" rate of 3,000 yen.

I tried to change the topic. "What's it like working out here, on this corner, at night?" I asked.

She huddled beneath her plastic umbrella, thinking. "Sometimes it's cold," she finally said. "Sometimes it's hot. Sometimes rain falls; sometimes the wind blows. Sometimes customers are mean; sometimes there are no customers at all."

Well, tonight it was cold, rainy and customers obviously weren't lining up. I could have hung around to talk, but the touts plying this street were shooting apprehensive glances over their shoulders and my instinct told me it was time to move on.

I stopped by a 24-hour convenience store for a bottle of mineral water and asked the bespectacled, uniformed teller about his job.

"With so many bars around here, I get drunks sleeping in my aisles," explained Satoshi Sugiyama, 22, as a customer discreetly flipped through a girlie magazine beside us. "Had to put one sleeper in an ambulance, once. Alcohol poisoning." A woman in heavy makeup paid for a pack of Doritos.

"Another time," he continued, "three foreign guys in suits -- they looked like secret-service police -- they came in here and asked me if the store was dangerous. I said, 'Well, I never had a customer go berserk or anything, but I do sell box cutters.' The guys inspected the premises really carefully, but ended up only buying cigarettes and soft drinks." He never did find out what the fuss was all about.

"Baffling," I said. "So why do you work these hours?"

"I want to be an actor, and it costs a lot to join the guild," he said. "The pay for nightshifts is better, so this is the shortcut to my dream. I've got about 70 percent saved up already."

I wished him luck and hit the pavement again. The end of my jaunt carried me down Aoyama-dori, along the leafy perimeter of the Crown Prince's Akasaka residence. It was about 4 a.m., and the sun's first rays were playing on the highest clouds. An elderly couple swept leaves near a playground while off-duty drivers slumbered inside idling delivery trucks.

With some embarrassment, it suddenly dawned on me that I knew this place.

It was either 1997 or '98, and I had drunk too much at the year-end party. As the last trains were pulling out of Tokyo, I was sleeping on a sidewalk somewhere, a candidate for hypothermia. Eventually, I got myself to a police box, where I asked the middle-aged officer to let me sleep in the back room. His rejection came swiftly, and I ended up plodding along in the cold along this very path, back to my office, where I crashed. I shiver just thinking about it.

Recalling the whole affair made me want to meet that officer again, to apologize for my unreasonable request years before. I made the 3-km trek to the police box.

Instead of that stodgy individual, though, a young, scrubbed officer in round glasses stood there, beaming with enthusiasm even at this ungodly hour. "Good morning!" he boomed. At a loss for what to say, I ended up telling him about my drunken episode. "That was my wackiest night in Tokyo," I concluded. "What was yours?"

"Ah, that would be the night I had my first corpse," he said, explaining that when attending a traffic accident on a late shift 18 months ago, he found that the driver had died on impact. "Every cop remembers his first corpse," he added with a nod.

We wrapped up our talk and -- ever effervescent -- he gave me a lively salute. Unsure how best to respond, I awkwardly saluted him back.

Sunlight was now filling the sky and I was famished after my seven-hour stroll. Walking up Omotesando in search of a McDonald's pancake breakfast, I reflected on the friendly people I'd met and the sights I'd seen. But McDonald's wouldn't open for another half hour, so I squeezed aboard a steamy, crowded Yamanote Line train and headed home. A man sneezed loudly without covering his mouth. Someone else shoved me from behind. Everyone looked miserable.