When you've killed Andariel and finished the main quest in the monestary you'll see a cut-scene. The next thing you do is to walk a round in a town in the desert Lut Gholein. The first quest you'll get is to find the tomb of Tal Rasha. This quest only takes place in the safe town Lut Gholein. The second quests takes you out in the hostile desert. In the dry desert you'll find catacombs, tempels, subterrain cities and hordes of monsters. New for act II are the level differences and the ability to walk inside of buildings. Act II will of course include new hordes of monsters and a crowd of new NPC's.