Key West, like most of the Keys, isn't the place to come for a day at the beach—the sand strips here are meager at best. But if you do want to take a break, hit the waterfront in the Fort Zachary Taylor Historic Site, which has picnic tables, public grills, and shady trees (305-292-6713; www.fortzacharytaylor.com). Be sure to bring sandals, as the beach is craggy pebbles. There is sand at Higgs Memorial Beach on the southern rim, as well as a volleyball net, palm trees, and picnic tables—this is also the unofficial gay beach.

These seven islands 70 miles west of Key West are a snorkeler's dream. The colorful coral reefs just a few feet offshore are populated by tropical fish and Queen conchs (there are free maps at the ranger's office). Back on land, you can tour Fort Jefferson, America's largest 19th-century coastal fortification. The fort was begun in 1846 but never completed despite three decades' worth of construction. It most famously served as a prison where John Wilkes Booth's unknowing accomplice Dr. Samuel Mudd was incarcerated (and later pardoned for his services during a yellow fever outbreak). The entire archipelago has also been designated a wildlife sanctuary to protect the nesting grounds of the sooty tern here; January is peak time for sightings.

There are two ways to reach the Dry Tortugas: by sea and by air. Taking the swoony 40-minute flight over the Gulf of Mexico is the faster but more expensive option (from $229 per person; 305-294-0709; www.seaplanesofkeywest.com). By sea, the high-speed ferry Yankee Freedom takes a couple of hours and can be choppy (bring Dramamine), but it's much better value ($159 per person including breakfast, lunch, island tour, and snorkel gear; 800-322-0013; www.yankeefreedom.com).

The Key West marina is packed with fishing boats available for charter. Dream Catcher Charters will take you out into the flats, the four-foot-deep waters around the Keys that are filled with tarpon, ladyfish, and barracudas (888-362-3474; www.fishingkeywest.com). For deep-sea fishing for amberjacks and cobia, Mr. Z Charters offers half, full, and even three-quarter day tours (305-296-0910; www.keywestfishtales.com). For snapper and grouper, head farther back up the Keys to Islamorada and call Richard Stancyzk at Bud'n'Mary's marina (800-742-7945; www.budnmarys.com).

An important backdrop for shutterbugs, this square and its famous rainbow sign mark the mile marker zero of U.S. Highway 1, 2,390 miles from its northern terminus in Fort Kent, Maine.

Originally a WPA project in the 1930s, this huge aquarium is swimming with barracuda, eels, parrot fish, stingrays, and other exotic creatures that live below the surface in Key West. Visitors can pet a live shark during daily feedings or hold a starfish at the touch tank.

This 19-acre site jammed into the center of Old Town dates back to Key West's 19th-century heyday, when the shipwrecking industry (salvaging goods from sunken ships) made it briefly America's richest city. Estimates put the cemetery's permanent residents at up to 70,000, most in vaults aboveground because of the high water table and solid coral bedrock that prevent the standard six-feet-under. The cemetery is both a fascinating time capsule—the opulence of some of the older graves underscores the town's onetime economic prominence—and an amusing catalog of Conch eccentrics. Look for Edwina Lariz, whose stone reads "Devoted fan of singer Julio Iglesias" and B. P. Roberts, who moans eternally "I told you I was sick." Pick up a guide to the graves in Walking & Biking Guide to Historic Key West by historian Sharon Wells (www.seekeywest.com).

Open daily sunrise to 6 pm.

The site of Key West's famous sunset celebrations also hosts a lineup of wacky street acts—a fire-eating family, jugglers, and a Houdini wannabe who escapes from a prison of chains. Not to be outdone, Dominick and his hoop-jumping cats perform nightly on the adjacent pier for the Westin Key West Resort.

There are two key shutterbug sites in Key West. Mile Marker 0, at the junction of Fleming and Whitehead streets, is a small green sign that marks the southern tip of U.S. Highway 1, a full 2,390 miles from its northern terminus in Fort Kent, Maine. The second is the squat red, black, and yellow barrel-shaped marker at the tip of South and Whitehead streets, which marks the closest you can get to the southernmost point of the continental United States (the actual point is part of a naval base). Word to the wise: Taking pics for tourists is a local moneymaking scheme, so the helpful people who offer their photography services will most likely expect a tip.

Don't be put off by the Errol Flynn–ish music piped onto the sidewalk and the hokey gift shop—this attraction is a trove of pirate treasure. Pat Croce (onetime president of the Philadelphia 76ers) and his daughter collected this impressive haul of more than 500 pirate-related items and now display it in a smart, engaging multimedia museum. Look for one of only two extant Jolly Roger flags as well as the only authenticated pirate treasure chest in the world. Adults will pick up fascinating nuggets like the fact that dandyish Black Bart was a teetotaler, but it may be scary for little ones: The disembodied animatronic heads and the superbly atmospheric room where Black Beard whispers the story of his demise into your headphones could shiver their timbers.

Open daily 9 am to 7 pm.

Just off Key West lies the only living coral-reef system in North America. You can see colorful coral, sponges, and starfish without ever leaving the mainland at Key West Marine Park, a protected swimming and snorkeling zone along the shore from Duval Street to the White Street Pier. If your sights are set farther from shore, Fury Water Adventures (305-294-8899) and Sebago Watersports (305-292-4768) make snorkel excursions out to the barrier reef. The six-mile trip takes about 30 minutes.