Your current mission's destination is [Phariseer's Tomb] located in the central part of the Dead Lands, and I definitely recommend planning the journey from the world map (the above screen). My suggestion is to fast travel to the [Maw] north of the tomb, which the exit of the previously explored Nook.
Once you're at the Maw, mount the horse and head south, using the bridge again. Keep going south until you see a large gate leading to the tomb, on your left (the above screen). Approach the gate and interact with it to get inside.