This is a huge pain - to find and to get to safely. The entrance to the elite Goblin-infested area is along the main north-south road at 23.8S 97.5W. It is NOT at the ruins, but slightly southwest of them, behind a barricade of shields and stuff. Now, proceed to a fork at 24.6S 97.5W and the take the uphill road to the left. This winds around a far ways until you get to 24.6S 98.0W where the entrance of Crookdell is. You will get credit towards the Exploration Deed here.
Fear not! You gain this exploration marker as part of the instance quest Assault on Rath Teraig :)