Let's play a little Jeopardy!, shall we? We'll take Geography for $500, Alex.

Answer: “It's considered the most remote national park in the lower 48 states.”

Lower 48 states, national park, remote — thinking, thinking, thinking. Well, it can’t be east of the Mississippi, and the West Coast is pretty much clogged up with civilization, too. It has to be in the heartland somewhere, probably up north.

Maybe in the empty frozen prairies. "What is Theodore Roosevelt National Park in North Dakota?" A wild (but good) guess. But while that is off the beaten track, it’s not the right answer.

Try Florida.

Florida? Yes, Florida. On top of that, the most remote national park in the lower 48 states is located in south Florida.

Beyond the silver high rises of Miami, beyond the gated communities and exclusive marinas on the Keys, beyond Hemingway’s Key West — land’s end — lies Dry Tortugas National Park.

The Caribbean coast without the crowds

Stretching the geopolitical limits of the U.S., a cluster of tiny islands, sandspits and shoals — some no more than a foot above sea-level — rival Caribbean vacation meccas. But they come without amenities, and therefore, without the tourists.

The shallow sea surrounding the Dry Tortugas shines turquoise from above, and is polished glass below. For those willing to make the long trip, small white sand beaches, tropical fish and unique 19th century history await.

For those willing to rough it, a nearly deserted tropical paradise and mind-bending night skies challenged by watery bioluminescence are on offer.

Go for the day, stay for the night

The name “tortugas” — Spanish for "turtle" — refers to the multitude of sea turtles that once plowed the waters surrounding the islands. The adjective “dry” was added to warn mariners of the lack of freshwater. Sadly, the numbers of turtles have declined dramatically, but the water situation has largely remained the same.

I started my boarding process pre-dawn, carrying gallons of water onto the dock at Land’s End Marina in Key West.

From Key West, it’s a 70-mile journey across open water to reach the Dry Tortugas. It's possible to reach the islands by seaplane, which offers great views from above, or by daily ferry.

The Yankee Freedom II provides day tours, and can also shuttle campers to the national park. The trip by boat takes about two-and-a-half hours, and an excursion for the day leaves visitors about four hours on the island — enough to wander the historic Fort Jefferson and do some snorkeling and sun bathing.

But day trippers miss the stars, the setting sun burning the Gulf of Mexico, and the quiet evenings. I planned to camp two nights, but soon wished I would have stayed longer.

From military service to park service

With my gear, water, tuna and crackers stowed, the ferry left the harbor after 8 a.m. and motored west. The catamaran skimmed across the azure water, a flat calm to the surreal morning. Halfway, we passed the uninhabited Marquesa Islands — thin strips of green hovering on the blue horizon. The stretch of shallow water that followed is favored by sea turtles of three species, and I saw dozens lolling on the surface, diving lazily as the boat's wake washed over them.

Fort Jefferson, an unfinished military bastion-cum-prison that was abandoned and then turned into a historic landmark, is the highest point, and by far the largest structure for hundreds of square miles. Construction began in 1846, and while the fort was nearly complete, it was never fully armed. It was eventually relegated into an army prison.

At its peak, it housed nearly 2,000 soldiers and civilians on an island less than a square mile large. Improved artillery rendered the fort obsolete by the end of the 19th century, and 100 years later, the islands, including the fort, were declared a national park.

The red brick walls of the fortification were visible for the last 20 minutes of the crossing. The ferry passed the gleaming sands of tiny East, Middle, and Hospital Keys, before anchoring at Garden Key. Fort Jefferson covers nearly the entire island, barely leaving room for the dock, a small picnic area and campground, and two crescents of sand.

Snorkel and saunter

I hauled my gear to one of the seven campsites and managed to snag a little shade under a small copse of trees and brush. Camping here is primitive — all food and water must be be brought with you, all trash packed out, and only pit toilets are available.

I had three days and everything to do. I snorkeled for hours, admiring enormous brain and stag coral. Kaleidoscopic parrotfish hugged the sandy bottom and hefty groupers hid beneath sunken boards. The wooden posts of the old coaling docks have turned into a garden of coral in the past 100 years, offering the best snorkeling.

Sea fans waved in the gentle current, and reef fish too numerous to count darted in and out. Swarms of tiny silvery minnows, so dense they decreased visibility to a foot, hovered between the pilings.

One morning I snorkeled out to the corals off the eastern beach, and suddenly found myself among a group of 30 tarpon — some of them five feet in length — as they searched silently for their next meal.

To dry off, I meandered in the fort. This immense, essentially inefficient bastion could only have been conceived by the U.S. government. With more than 16 million bricks, it represents the largest masonry structure in the western hemisphere.

I walked to Dr. Samuel Mudd’s cell, one of the prison's most famous prisoners for his involvement with the assassination of President Abraham Lincoln. I wandered along empty halls and took a narrow spiral staircase to the top of the wall. The three-tiered structure was supposed to house hundreds of artillery, protected behind brick and mortar up to eight feet thick.

Today, a few relic cannons are on display. A moat protects the hexagonal outline of the fort — from enemies in the past, from hurricanes today.

Standing next to the lighthouse, black metal under the fierce sun, I looked north. Tens of thousands of birds wheeled, screeching, above nearby Bush Key. Every year 70,000 seabirds come to this remote spit of land to raise their young.

The invertebrates come out at night

The island grew quiet after the day trippers left (except for the birds squawking), the small beach emptied, the heat relented and the scene perfected itself for a sunset swim. I watched the last of the sun cool from white to yellow to deep orange and sink just to the west of distant Loggerhead Key. Fort Jefferson closes at sunset, leaving campers to take night walks along the moat wall, read or stargaze.

I strolled along the moat under a night sky unblemished by light pollution. Instead of single stars, it looked like glowing dust blown into black.

Staring into the inky water below, I noticed flashes, like weak blue neon. I looked closer and saw them again, more and more.

It took me awhile to figure it out what was happening. Apparently, inside the shallow warm water of the moat, bioluminescent invertebrates had been concentrated, and the quick spurts of fish large and small disturbed the water enough to make them glow.

The national park doesn't permit swimming or snorkeling in the moat. But the next morning, I talked to a fellow camper who could not resist the lure of the light. He said he had walked into the shallow luminous water, next to a large fish that left thick streaks of bluish light. Then he dove into the black that broke into specks of bright ephemeral flakes around his hands. Almost like exploding glass under a bright sun, but soft, he'd told me.

Yet after 30 seconds of this phantasmal reverie, it became apparent why swimming in the moat was not recommended. In addition to aggregating effulgent siren-like creatures, the water also contained a high density of jellyfish. Distinct burns on his arms, legs, and more sensitive regions roused the fellow camper from his dreamlike swim.

He scrambled back onto the beach. "It was worth it," he said.

The Dry Tortugas are more than worth it. The park offers the chance of remote camping, world-class snorkeling and pristine waters with hardly any effort or cost. I am already making plans to return and stay longer.