America's only all-water cavern isn't just a cavern -- it's a wildlife park, too.
Penn's Cave and Wildlife Park (222 Penns Cave Road, Centre Hall, Pa.) offers one-hour guided tours by motorboat in the caverns, and has thousands of acres of preserved natural habitat with plenty of fierce animals to see.
During the 50-minute boat tour of the caverns, you'll travel through passageways with the ceiling of the caverns 1,300 feet above you. Check out stalactites and stalagmites that appear in "mysteriously familiar shapes," including the Statue of Liberty and the Garden of the Gods, plus impressive pillars, cascades and massive columns.
When you get back outside, join up on a 90-minute farm and wildlife tour, hop a bus and travel across 1,500 acres of land, where you can get up close and personal to with some bears, bobcats or wolves. OK, maybe just look at them. From afar.
A combo ticket (cave and Wildlife tour) is $30.95/adult; the cavern only is $16.95. You can also try gemstone panning, at $5.50 for a small bag, $10.50 for a large bag. Bring a sweater or jacket for the cavern tour.
Centre Hall, Pa., is about four hours from downtown D.C.