Go to the tower | Penal Colony - Barry RE: Revelations 2 Guide

In spite of low threat, it is best to eliminate the spiders fast

You start at the docks. Together with Natalie, head towards the stairs, at which to go left. Head along the rocks and smash the crate and the bottle, as you go., where you find pistol ammo SMG ammo. A bit ahead, you will be attacked by three mutated spiders that you will quickly defeat in melee. Then, climb onto the ledge above, where you receive the flashlight ([Z]). Head on, between the rocks and finally, you will get to the very top.

The emerald is right under the ceiling- shoot it down and pick it up

Here, you will be attacked by several spiders. After you go left, towards the gate blocked with containers, you find a Tower Emblem. In the small dilapidated building, use the flashlight to locate Emerald on the upper part of the wall (1000 CP, shoot it down). Then, approach the main building.