Perched in my Fairmont Hotel room atop Nob Hill, I look down on the San Francisco Bay and watch a searchlight slice through the night sky. Every five seconds it swings across the water beneath my aerie. It is the searchlight on the deserted island of Alcatraz, wrapped in fog and steeped in legend.

There is something hypnotic about a searchlight, something especially entrancing about one stationed on an island that cased the most incorrigible criminals -- animals, some said -- in the country.

I first visited Alcatraz -- San Francisco's second most popular tourist site after the Golden Gate Bridge -- 10 years ago, and have returned three times. The first visit was prompted by the island's history and the chance to take a boat across the water on a sunny day. But I returned because of the way the place makes me feel.

Alcatraz promotes contemplation and inspires wonder. It has a severe feel of finality about it, perhaps because the prison was the last stop in many men's lives. The empty prison makes you think about evil and violence. A visitor can almost taste the desperation and loneliness that must have overflowed its thick walls and driven some of its residents to risk escape; even though its inmates knew the odds against surviving the cold and powerful currents of San Francisco Bay, six died trying to swim to freedom.

A few months ago, I learned that a former Alcatraz guard lived in San Francisco and liked to talk about his old work place with visitors. Today, Frank Heaney, 60, once the youngest guard at Alcatraz, does public relations work for the Red & White Fleet, the ferry that carries tourists between San Francisco and Alcatraz.

As Heaney and I board the boat to Alcatraz, the rain begins. It is a cold rain. The temperature is unusually cool for afternoon, the sky uncommonly gray.

Heaney gets it right: "Kind of an Alcatraz day," he says.

Once, the island was a barren 12 acres of sandstone and granite, which is why it's called The Rock. Then, in the mid-1850s, Army engineers hauled soil and vegetation from a nearby verdant island and built the West Coast's first lighthouse. Over huge stone cisterns that held fresh water brought in by ship was built a fortress with long-range cannon to protect the entrance to the San Francisco Bay. At the turn of the century, the War Department began housing military prisoners there.

In the '30s, all hell broke loose on the crime front in the United States. Killers such as John Dillinger and gangsters like Big Al (Scarface) Capone became little kings. Gang murder as well as prison riots and escapes became alarmingly frequent. What the Justice Department needed -- and found in Alcatraz -- was an isolated prison ideal for jailing as many as 300 of the nation's worst offenders.

"We had the most incorrigible prisoners," recalls Heaney, who went to work there at age 21 in 1948. "No one came here from the courts -- they were all problem inmates from other federal and state prisons. All bad apples."

Among them were Capone, George (Machine Gun) Kelly, Alvin (Creepy) Karpis, and the man over whom Heaney watched, Robert Stroud, a murderer better known as "the Birdman of Alcatraz." Stroud gained fame thanks to a movie that focused less on his heinous crimes and more on his hobby of breeding and studying birds -- at one time he had almost 300 of them in three cells at Leavenworth prison in Kansas. He was transferred to Alcatraz when he killed a Leavenworth guard.

As the boat docks at the island, a sign at water's edge reads: "Warning: Persons procuring or concealing escape of prisoners are subject to prosecution and imprisonment." To the right looms a guard tower. A zigzag cement walkway leads to the prison.

We enter the prison the way the prisoners did, through the room where inmates took their twice weekly showers in groups of about 25. Rectal exams of incoming prisoners, Heaney says, sometimes turned up hidden sleeping pills and pieces of hacksaw blades wrapped in paper coated with petroleum jelly.

Upstairs are the main prison cells, including the infamous D-block solitary cells, with 200-pound steel doors that close to shut out all light. Once green, D-block was ordered painted pink by a warden who said a psychiatrist told him pink was a soothing color.

Inmates earned a room on D-block for days or weeks by breaking prison rules. An inmate who tore up his clothes or bedding was locked in the dark, naked, in the single "strip" cell, which had no sink or toilet, only a hole in the floor. Until the practice was halted by court order in 1939, the worst offenders were stashed in the "dungeon," old Army storage areas beneath the prison where inmates, sometimes chained to the wall, were confined in damp darkness.

The main avenue in the center of the prison was called "Broadway"; it was the coldest part of the prison and afforded the least light. The prison was segregated, and black prisoners (about one-third of the prison population in the '50s, half in the '60s) did their time on Broadway.

The paint inside Alcatraz is peeling now, but Heaney says the place was once kept shiny as a new dime. The food was "monotonous, starch, and generally steamed," and he should know: the guards ate the same food as those they guarded.

There were eight manned gun galleries and towers around Alcatraz, and guards in each one had to check in by phone with a control center in the cell house every 30 minutes. Alcatraz rules were the nation's most severe. Prisoners were allowed no candy or cigarettes. They could read only approved books and transcripts of their trials, which they studied in hopes of finding grounds for legal appeals. They were paid 25 cents an hour for working in the prison laundry or in the factory that turned out brooms, brushes and Army uniforms for the General Services Administration.

Inmates were permitted a single 1 1/2-hour visit once a month; all conversations were conducted through telephones and monitored by guards to make certain only family matters were discussed.

Today, many of the island's smaller buildings -- the workshops, correctional officers' barracks, family quarters and the warden's house -- are shells. They were largely destroyed in 1969 and 1970 when American Indians focused national attention on their grievances by occupying Alcatraz for 19 months.

But the centerpiece of Alcatraz, the prison, still stands, a bleak house whose isolation spawned stories of torture in the popular press earlier this century, and whose notorious residents and their escape attempts inspired movies. Heaney admits that guards -- they called themselves officers; the prisoners called them "hacks" or "screws" -- sometimes used (illegal) blackjacks to subdue rampaging inmates. But he denies that more Draconian tactics were used.

In the prison, courteous National Park Service guards lock tourists inside D-block isolation cells. Most visitors, they say, get uncomfortable after about 60 seconds in the dark; imagining a week or more seems impossible.

But even in the toughest prison in the United States, hope sprang eternal. Heaney says periodic shakedowns produced surgical gloves and hot water bottles meant to be used as flotation devices, as well as homemade snorkels, shivs, shanks, knives and even zip guns fashioned out of tubes, chipped match heads and rubber bands.

During Alcatraz's history, 39 inmates made 14 unsuccessful escape attempts. Some were shot dead, some drowned.

The last escape attempt, in 1962, was almost successful. Inmate John Paul Scott and a coconspirator spent years loosening the bars over a storeroom window using twine soaked in wax and covered with cleanser. They managed to climb out and down to the water.

His sidekick made it only 50 feet to a rock, but Scott managed to avoid drowning or being swept out to the Pacific Ocean. However, he almost died of hypothermia in his struggle to swim to the mainland. A couple of teen-agers spotted him in the surf near Fort Point and alerted police. When he was dragged ashore, Scott was near death.

You think of these stories when you walk through the still prison, either with a group guide or by yourself. Along the walkways and service roads of the island are Monterey cypress and fragrant eucalyptus trees. To the south is a great view of the San Francisco skyline.

Frank Heaney began work as an Alcatraz guard because he had watched Pat O'Brien and James Cagney movies and was fascinated by tales of crime -- "some screwy thing in my head," he says today.

Everyone told him he was too young, he wasn't tough enough to guard the big boys who knew how to antagonize new hacks. But he stayed, quitting after three years to join the Navy. As a civilian, he made a career as a firefighter for 27 years and raised three daughters.

Heaney says his wife can't bear to hear him tell Alcatraz stories, but he never seems to tire of answering the same questions from tourists whose romantic notions of Alcatraz were shaped by Clint Eastwood and George Raft movies.

As a prison, Alcatraz was closed because it was deteriorating in the salt air, San Francisco residents didn't like the place dumping untreated sewage into the bay, and one hardy prisoner had proved it was at least possible to swim to the mainland.

If Alcatraz had been located on the mainland, it probably would have been forgotten. There hasn't, for example, been much attention paid to its replacement, Marion Penitentiary, in Marion, Ill.

But because Alcatraz is out there jutting above the angry water, its silent searchlight still sweeping the bay, it holds the imagination.

Once again, Heaney gets it right: "There are as many crooks now as then," he says, "but they'll never be so romanticized."

Rudy Maxa is a senior writer at Washingtonian magazine.