Tough question, Scott. You could practically fill out a list like this for each individual national park--except maybe the piddly Cuyahoga National Park outside of Cleveland, which became federally protected in 1974 (to give refuge to rats in the Erie Canal there, I guess). Anyway, here's my list of five national park adventures to do before you die.
Watch the Sunrise in
Acadia National Park, Maine
Stand atop 1,500-foot Cadillac Mountain in Acadia at dawn in the fall, and you'll be the first person to witness the sunrise in the continental United States. Then spend the rest of the day exploring the rustic coastal wonder of the country's most underappreciated national park.
Overnight at Glacier Point in Winter, Yosemite National Park, California
Glacier Point, which overlooks Yosemite Valley and Half Dome, is as crowded as the castle at Disney World in the summer. But in the winter, you've practically got the place to yourself—as long as you're willing to cross-country ski 10.5 miles through the backcountry to get there. The coolest part: you can bunk, and get a hot dinner, at the Glacier Point Hut there if you make reservations in advance. ($120 per person)
Sled the Silicon Slopes of
Great Sand Dunes National Park and Preserve, Colorado
Great Sand Dunes is the country's newest national park, and maybe most novel. As you trek among the towering sand ridges—which rise as high as 700 feet—you feel like you're in the Sahara. They also make for once-in-a-lifetime sledding, even when there's no snow. As long as you use a flat-bottomed plastic sled, and go after there's been a little bit of rain, you'll scoot down the hills like Clark Griswold on Christmas Vacation.
Soak in the Bubbling Waters of Hot Springs National Park, Arkansas
Even Hernando de Soto and his gang made their way to the hot springs beneath the Ouachita Mountains of central Arkansas to see what the fuss was all about—in the 1540s. They had such a good time that they lingered there a few months, legend has it. The land there now is the oldest federally protected preserve in the country, and its 900 acres encompass 26 miles of trails and the historic Spanish Colonial and Mediterranean-style buildings of Bathhouse Row within of the town of Hot Springs itself. Soak in a private mineral bath at the Quapaw Baths & Spa. Roughing it in a national park can't get any more luxurious. ($30 per person, or $45 for a couple for the mineral bath,).
Kayak in the Florida Everglades if You Dare
At 1.5 million acres, Everglades National Park is the third-largest national park in the continental United States. When you paddle among the mangroves of the Gulf Coast, you're seeing subtropical Florida at its most majestic and untamed—as long as you don't mind occasional alligators, snapping turtles, and water moccasins.