As for the end goal, you have two objectives: cleanse the dungeon of all enemies, and destroy the big statue found in a circular room with a domed ceiling (referred to as The Statue of the Black Monk). Killing all the enemies is straightforward, however there’s a subtlety regarding the way to destroy the statue: a player tends to automatically assume that weapons will do the job, but in fact you are required to jump on the plinth to touch the statue and thereby destroy it. This puzzle-like feature is not intuitive and the map is average in terms of difficulty because of that (I was stuck for a while because of that – whereas the fighting itself is easy). Once you’ve accomplished those two objectives, you have to return to the tower where the ghost of Alin’Gar’s son is, and you will see that he is now free; a doorway opens up and a last message thanks you for your help, before inviting you to take a portal that will take you on to new adventures… and thus you reach the map’s exit 🙂
Hope this helps!