I know that a hole through the earth wouldn't work because it constitutes perpetual motion. But what exactly would stop you from falling, reaching terminal velocity, falling the other direction, reaching terminal velocity again and oscilating like that forever? It couldn't be friction, air doesn't stop you from reaching terminal velocity if you jump out of a plane. Does terminal velocity not bring you far enough into the other side of the earth to reach it again?
Long post, I know.