When you enter Shadow Pass, located south from High Fulgen, the first NPC you will encounter is Desiderus Trav, the quest giver you have met earlier.
Side Quest: The Killing Ground
Objective: Meet Desiderus Trav in Shadow Pass
Desiderus wants you to reach the final Tuatha Encampment and kill the Tuatha Commander, the Witch Knight named Dessidyn. The encampment and Dessidyn are located on the main road that takes you to Twilight Pass.
Unlike other Tuatha bosses you have encountered, Dessidyn is weak against magic. Assuming that you have reached the maximum level by now, this fight will be easy, even if Dessidyn seems to be a strong opponent.
What you should do, is to get rid of the Tuatha Priests in the camp, and then focus on the boss. If you play as a Nightblade, try to push him back near the fire, and there using a set of daggers or Fae Blades, attack him.
Even if you wont be able to earn additional XP points, remember that in Reckoning Mode, your stats are increased, which means that the amount of damage you inflict is higher.
If you cant enter Reckoning Mode, drink a Greater Damage Boost potion for a similar effect.
Kill Dessidyn then talk to Desiderus Trav, to complete The Killing Ground side-quest.
At this point you should continue your exploration, but you will notice that you cant start any side-quests, since Desiderus Trav is the only quest giver. The points of interest you should have on your map are Mordus-Torr and Glowlode Cavern.
Mordus-Torr is a straight dungeon, featuring three exits. Practically, these exits allow you to reach other areas, behind the enemy lines. Explore them for additional items and gold.
On the other hand, Glowlode Cavern features only one entrance, which is hidden. The exact location of this dungeon is on the eastern side of the area, inside the mountain.
To find Glowlode Cavern you may need to increase you Detect Hidden Skill (5 or above). After you discover it, enter and explore it, focusing on the eastern side of the cave, where you will find Esha. Talk to Esha and you will start a quest named after her.
Side Quest: Esha
Objective: Escort the Survivors
After you start this quest follow Esha and help her and the Ashmoor survivors escape Glowlode Cavern. Kill all Murghans and the Cave Banshaen that spawn in the cave trying to stop you, and when you reach the exit speak to Esha again, to complete the quest.
Now, it is time to go deeper into Alabastra, and enter the next area, named Twilight Pass.