Gunther's Cavern

Crazy wishes don't come true—do they? And if they do, might you later wish they didn't?
Almost 16, Gunther finds life on the edge of the Catskill Mountains to be beyond boring. If only a replica of Coney Island's Cyclone would appear overnight behind his house, or a cave would open up in the far reaches of his family's run-down farm, his life would be so much more interesting.
But a cave does open up, and the entrance caves in after he and his younger sister June have entered. Traversing the cave looking for another way out, they find that the cave is populated by tardigrades that have evolved over many centuries from 1.5mm microscopic specimens to four-foot high, intelligent creatures. They find, too, that the tardigrades have captured a dozen fellow high-school students who have unknowingly wandered into their cave via another entrance.
Even while the young humans, led by Gunther and Hood—formerly one of Gunther's least-favorite classmates—attempt to maintain peaceful communication with their captors, they work on a method of escape. To escape, they must not only evade the tardigrade army, but deal with the team of giant insects that guard the exit.