If the Square's madness starts reaching a dangerous crescendo, if the Organic Chemistry starts looming up all around, if your summer roomie is a lunatic, then you only need drop out of sight into the subway station, drop a quarter into the slot, and leave Harvard behind. It's cheap escape.

The Red Line trains that will shoot you down under Mass Ave are the top of Boston's subway fleet. The Red Line has the plushy-cushioned seats, and it has the milk run through the city from the local (elitist) seat of higher learning to the local pseudo-quaint suburban town of Quincy Center. The Red Line is good for long, dark rushes under the streets, but is also boring. Its best feature is on board--the spectrum of people riding between the Square and Boston. But beyond Washington station the passengers get boringly respectable and well-dressed.

High points on the ride are few. Central Square is worth checking out just to discover that Cambridge is not all Ivy and academia. Kendall is nowhere, halfway between the Necco candy wafer factory and MIT. But after Kendall the train crosses over the Charles, offering one of the best views of downtown Boston (and the river itself) to be found. The Charles-MGH stop is not worth debarking at, although conversation-wise you should remember that it stands between the largest hospital in New England--Mass General--and one of the few neighborhoods in America still using gas street lights.

After Charles-MGH, the train plunges under Boston. When it emerges blinking from the other side of the city a few stops later, it has a long, pleasant, dull ride down to Quincy.

If ivy and ivory towers do not appeal to you, get off the Red Line at Washington, and take the Orange Line south. The train surfaces quickly, and from its elevated track on slanting and creaking wooden beams the train offers a view of an area easily ignored by those who only see Boston when they shuttle from Harvard to the airport or the Amtrak station. The area is very poor and very black. One ride from Washington down to Forest Hills is the best reminder that ours is not the best of all possible worlds. Forest Hills, the end of the line, is on the edge. North lie graffitti and broken glass. South stand houses and big old trees on thick lawns. Stand in the middle and figure it out if you have the stomach for this kind of paradox.

The Orange Line also extends up into Everett. Forget it. Oak Grove, the wrong end of the line, is a residential wilderness.

The Green Line is the most distinctly Bostonian of the four iron mole lines. The tracks make crazy turns, the cars' wheels screech terribly, and the cars are too small--more streetcars taken underground than proper subway cars. The passengers are nearly a cross-section of the city's population. With stops at Northeastern University, Boston College, and at least a dozen other schools, the Green Line gets plenty of students, but it also gets much more than the 19-to-27 crowd that sometimes starts to seem like the only possible age group in the Square--it's a major boon to Boston's sense of community.

The aboveground ride out to Riverside is probably the best in the system. It is one of the few stretches of track on which you can tell the season by the color of the trees as well as the outergarments of the other passengers. The Green Line's cars are throwbacks to the days when streetcars ruled Boston's thoroughfares, and the swerving, stop-and-go trolley route to Arborway is one of the last true streetcar routes in town. The ride may be pure agony to the impatient, but the Arborway stop at the end of the line is just a short walk from the entrance to the Arnold Arboretum--a Harvard-owned park that supposedly has every kind of plant that will grow in Boston's climate. And they have some bizarre growths. The woody, rolling hills there are the farthest back-to-the-woods you can get by subway.

In the other direction, the Haymarket stop near the North End is worth getting off for. At the market vendors offer fruit and vegetables from open wooden carts on the street, which is always covered with at least a day's layer of garbage. Good deals are available there, but watch out for the hucksters who will slip you a bag of rotten peaches from behind their stands in place of the perfect peaches enticing you out front. It is wise to go in the evening, when the sellers want to go home and will therefore sell whatever they have left for small change. Acorss the highway from Haymarket is the Italian North End, complete with good restaurants, tight ethnic community, and Old North Church. But don't wait for some short, dark-haired lad to come running out of an alley shouting that it's "Prince Spaghetti Day." They only eat that shit in Quincy Center.

All of the Green Line stops have some distinct personality and bear checking out. The line is a good bet for a safe return on that quarter investment, although here, as on the other lines, you have to ante up a quarter more past a certain distance.

The Blue Line holds the most exciting ride, roaring through a tunnel under the ocean, coming up for air by Logan Airport, and then running out along the shore to the north. Most of the stations have clever motifs--the Aquarium stop has, oddly enough, huge line shots of fish on the walls. The Airport stop has line shots of jet airplanes, and past the Airport stop the train rattles by hangars so you can get a close look at the big birds themselves.

Near the end of the line is Revere Beach. On a cool night Revere Beach means fried dough, pinball machines, dark bars, leather-jacketed adolsecents, pizza, joints, dirty sand, dirty ocean. On hot days people actually try to use the beach, although the ocean there is about as swimmable as Cambridge water is directly drinkable. But Boston's decaying and dinky answer to Coney Island is nonetheless high on liveliness.

The end of the line is Wonderland. Go explore it yourself.