Witcher 2, The - Assassins of Kings Message Board  

(Vergen, I think?).

There are 2 exits to this town, the big main gate and a separate exit.

To get to the 2nd exit (that leads to the woods etc), you head to the main exit gate and instead of going out, head up the steps to the right of it (as you are looking out of the gate, still inside the walls. Follow that around to the right and you'll find the Old section of town, lots of huts. Heading along that street will lead you to a tunnel to the North that takes you out of the city

You need to to go to the front of the town, near the giant gate, there is stairs leading up the north side, keep on heading north, pass the boarded up part of town, then through the cave tunnel. Next cross the river at the shallow south part, and once on the other side, head north along the rock path and back to the river, passing a small pond, at the rivers edge, there is a ramp leading to the top of the rocks, jump across a few ramps, kill harpies and then inspect the nest and take crystal.