FORT DRAKON
Entrance
You'll start the game in front of the fort (Denerim Fort Drakon Map, L1) and you should summon one of the armies as soon as possible. I would recommend choosing human or dwarven warriors to assist you in dealing with enemy archers hidden behind barricades. You on the other hand should focus on killing one of the smaller dragons at the same time. Once the beast has been eliminated start attacking other powerful creatures, including new hurlock emissaries. Keep fighting until you've defeated all hostile units and then click on the main gate of the fort (Denerim Fort Drakon Map, L2) to travel to Denerim Fort Drakon Main floor (Fort Drakon Main Floor Map, L9).
Main Floor
The biggest battle is going to take place inside the main room of the fort (Fort Drakon Main Floor Map, L14) which is going to be located to the south of the area where you've started the game. Watch out mostly for shades, especially since you'll encounter at least one mini-boss. Once the demons have been defeated start attacking a genlock conjurer (main boss). Head south once it's safe again to move on with the mission (Fort Drakon Main Floor Map, L11).
Keep going straight until you come across a large trap which must be disarmed. Get ready to defend yourself against a large group of the undead (Fort Drakon Main Floor Map, L15). You'll also have to watch out for two mini-bosses at the same time - an emissary (kill it as soon as possible) and a shapeshifter. Don't forget to loot bodies of fallen enemies for possible treasures, as well as to search nearby rooms. Head to the eastern warehouse (M79, 6) once you're done exploring. You'll meet Sandal here (Fort Drakon Main Floor Map, L16) and make sure to talk to him, because this will be your last opportunity to barter or to enchant weapons before the final battle takes place. Choose the passageway found behind his back to travel to Denerim Fort Drakon First floor (Fort Drakon 1st Floor Map, L17).
First Floor
This time you'll begin in the north-western section of the fort (Fort Drakon 1st Floor Map, L1) and you'll have to start moving east until you enter a room with two exits (Fort Drakon 1st Floor Map, L2). Exploring the eastern room is optional - you would come across a lot of archers and after defeating them you would have a chance to look around. You must use the southern passageway if you want to get step closer to meeting the archdemon. Be careful here, because the next corridor contains a lot of traps and you'll be attacked by assassins, including a genlock master assassin. Prevent the creature from dealing too much damage and don't fight the genlocks near the traps to avoid potential trouble.
Once you've dealt with all assassins make sure to ask your rogue for help in disarming all of the remaining traps. You may now begin moving south until you make your way to yet another large hall (Fort Drakon 1st Floor Map, L3). Attack the two ogres seen in the next room from a distance to make them chase you and stand somewhere near the door to fight with only one beast. Thankfully your team should be skilled enough by now to challenge even two ogres at the same time, but you should play it safe. Once you've defeated both ogres enter the large room again and this time focus on killing the emissary. Before you travel to Denerim Fort Drakon Roof (Fort Drakon 1st Floor Map, L4) make sure to SAVE your game and to check nearby chests for additional treasures (Fort Drakon 1st Floor Map, L5).
Now head on to the Big Boss Battle Archdemon Urthemial.