It’s possible for a New Yorker to go weeks without glimpsing a river or a harbor, and to lose track of the fact that Manhattan is both an island and a seaport. This misapprehension is inconceivable, however, for a user of the Waterfront Greenway, a well-marked thirty-two-mile route for walkers, runners, skaters, cyclists, and other non-motorized travellers. It follows the Hudson, Harlem, and East Rivers around Manhattan’s perimeter, with occasional inland detours (across Dyckman Street, way up beyond the Cloisters; along the spine of central Harlem; around a couple of dozen blocks near the United Nations). The Greenway is especially well suited to bicyclists, who, if they are moderately fit and don’t blow a tire on a broken apricot-brandy bottle, can cover the entire distance in a single leisurely morning or afternoon. Biking the Manhattan shoreline turns the city inside out, and gives the cyclist firsthand answers to questions that often stump even lifelong residents, such as: are there any decent places in Manhattan to go rock climbing, and what the heck do they keep under the Henry Hudson Parkway? Perhaps you yourself rode the Greenway on a recent, spectacular Friday afternoon, beginning and ending at the Battery, where, when you started, a man wearing a broad-brimmed hat was baiting a fishhook with a half-dollar-size crab, which he had selected from a joint-compound bucket at his feet. If so, here are a few of the other things you may have noticed along the way:

Helicopters and small airplanes flying above the Upper Bay like dragonflies above a swimming pool.

A man wearing a black wetsuit and an orange life jacket, bobbing in the Hudson about fifty feet from shore, using various hand tools to affix four large pink plastic petals to a rotting wooden piling. According to another man, who was standing onshore and holding a walkie-talkie, the man in the water was “installing prototypes for an art project, to see how they make it through the winter.”

The Parthenon-like and perhaps spectacularly luxurious colonnaded rooftop outdoor lounging facility of Larry Flynt’s Hustler Club, at Fifty-first and Twelfth.

A guy who had been shooting hoops alone on a court underneath the West Side Highway asking another guy, who had been shooting hoops alone on a different court, two courts away, for a little help in retrieving his ball, which had become stuck between the rim and the backboard, and then also asking, “Wanna play?,” and then the two of them continuing to shoot hoops alone but now on courts adjacent to each other.

A man in bluejeans travelling south on a bright-yellow pedicab piled high with driftwood, which presumably he had collected along the river’s edge, steering with his right hand and using his left hand to give his left leg a downstroke power assist; and a middle-aged nun in a white habit, veil flapping, riding a regular bike in the opposite direction.

A lost or discarded parking ticket undulating like a miniature magic carpet in the tiny waves a few feet from shore.

A guy fishing with an enormous surf-casting rod a little downstream from the George Washington Bridge and around a bend from the Jeffrey’s Hook Lighthouse, which was saved from demolition in 1951 by outraged readers of the children’s book “The Little Red Lighthouse and the Great Gray Bridge,” by Hildegarde H. Swift and Lynd Ward.

Several hundred pigeons loitering near the center of an otherwise unoccupied playing field, and, on the other side of the bike path, a man in running clothes sticking out his lower lip while doing rapid, shallow pushups on a bench.

A trailer, carrying rowing shells, parked near the magnificent gate of the Peter Jay Sharp Boathouse, in Swindler Cove Park, on the Harlem River.

The turreted, thirty-room 1887 mansion of James Anthony Bailey, who was the co-founder, with P. T. Barnum, of “The Greatest Show on Earth.” The mansion, which is at the northeast corner of 150th Street and St. Nicholas Place and is made of limestone, inspired Chester Wickwire, who may or may not have invented the woven-wire window screen, to build an almost identical mansion in Cortland, New York, in 1890.

Four old guys watching four other old guys eating slices of pizza at a white plastic card table on the sidewalk at 120th and First.

More bollards, cleats, capstans, hoists, and other riverside mooring paraphernalia—some of it freshly painted—than you would think could possibly have an ongoing nautical application in New York City.

A young man transporting a set of golf clubs—which he had stuffed vertically into his bicycle’s saddlebags—toward Stuyvesant Town.

Three young women from a country where the shoes don’t look like ours, on a walkway above what may be the only sandy beach in Manhattan (under the western end of the Brooklyn Bridge), heading north from the South Street Seaport area, on their way to their next big adventure. ♦