Maybe Close

My idea of a really tough one would be a cache with a small, weak flashing light inside a pipe. The muzzle of the pipe would point towards the given coordinates, some hundred yards away, and between the coordinates and the cache there would be some kind of obstruction, a lake or a steep hill. You'll have to be there in the dark to see the light, and you'll need to do the swim/climb thing in the dark. And maybe one should throw in some sort of code for good measure. Übertricky.