Above us on a warm spring day, the early jonquils are blooming and trees are just beginning to bud. But where I'm at, some 500 feet beneath the earth motoring quietly along Myst'ry River in Bluespring Caverns, the only form of life in the high-vaulted limestone passageways are strange albino crayfish said to have lived here for eons and a few bats said to live in the ceilings above.

The river winds through subterranean passageways whose sides are edged with sculpted walls dotted with ledges and dark holes leading into deeper passages. The strangely beautiful and surreal stalactites and stalagmites formed slowly by endlessly dripping water.

Our hourlong boat tour traverses just a few miles of this river, the longest navigable underground river in the U.S. Although it's currently measured at 21 miles with much more still to be explored and mapped, our trip covers just a few miles. When the boat turns around, blocked from going farther by monolithic formations, I glance backward and watch it flow on into the dark.

Underneath the rolling hills of Southern Indiana is a complex system of caves thought to number more than 2,600. Only four are easily accessible and open to the public, and each is unique and wonderful in its own way. I find this out as I explore another: Marengo Cave, a tourist attraction since 1883. That's when 15-year-old Blanche Hiestand convinced her 11-year-old brother, Orris, to scramble down a sinkhole and crawl into the small opening of a cave, their only light coming from the two candles they carried.

Now fortunately an expert in cave lighting has creatively disguised lights, something I don't catch on to until our guide points out that a small dripstone formation is really a light. Easily navigable walking trails take us through large cave rooms with names such as Crystal Palace and the Gothic-looking Music Hall with its twisted, intricately water-carved rocks. Here we sit on stone benches, listening to music while watching lights cast the cave's contours in myriad colors.

The tour takes us past two underground lakes — Looking Glass and my favorite, Mirror Lake, because when you look into its placid waters, the reflection of the cave creates the illusion of another room far below.

BLUESPRING CAVERNS, 1459 Bluespring Caverns Road, Bedford, Ind., 812-279-9471, bluespringcaverns.com; MARENGO CAVE, 400 E. State Road 64, Marengo, Ind., 812-365-2705, marengocave.com; indianacaves.com

Wild Woods

Adventure awaits on the Canadian coast of Lake Erie. Set amid 15,000 acres of Carolinian forest, crisscrossed with zipline cables and miles of hiking and mountain biking trails, Long Point Eco-Adventures has quickly become a desirable destination for active outdoor pursuits, whether you come for the day or stay overnight. All-inclusive packages with lodging, activities and meals start at $415.99 per person. Long Point Eco-Adventures, 1730 Front Road, St. Williams, Ontario, 877-743-8687, lpfun.ca

Get your blood pumping with a zipline and canopy tour that lets you soar high above the forest floor for more than two hours. The tour includes eight ziplines, two suspension bridges, 14 treetop platforms and a 40-foot rappel that brings you back to earth. Amp up the adrenaline with nighttime ziplining on Friday and Saturday. Prices start at $95 for adults, $75 youths (ages 8-17)

Brand new wilderness suites give guests the opportunity to spend the night in luxury tents overlooking Turkey Point Marsh and Long Point Bay. Each is equipped with unexpected comforts, such as lots of headroom, indoor plumbing and a choice between of one king-size bed or two doubles. Prices start at $229 per night, including continental breakfast

Spend a day paddling Big Creek, also known as the "Canadian Amazon," which meanders gently toward the marshes of Long Point Inner Bay. The guided adventure includes a kayak or canoe rental, life jackets and dry bags to keep your camera safe. Prices start at $75 for adults and $45 youths (ages 8-17) for a half-day tour, $95 and $65 respectively for a full day.