Upward Bound

Feel the shock of an icy waterfall — two fists of crystal froth, crashing down a granite wall, framed by a tangle of vines. With a rope secured around your waist and anchored to the top of the rock, you start rappelling, creeping backward down the 150-foot vertical face. You're in the heart of the Costa Rican jungle, feeling helpless on these massive rocks, trying to manage your fear — and not to look down. But you're not alone. Below, one of your colleagues is anchored to terra firma,