You cast the spell, and tug and push on the door again. Finally, it opens inward so quickly that you nearly tumble down the stairs.
This part of the tower has no windows, since it leads underground. You light your lantern. The light bounces off the walls and flickers on the dust and cobwebs. Definitely not the busiest place in the world.
You start down the stairs, one step at a time. It smells musty and unpleasant. The stairs seem to wind down forever, but finally you come out in a large, stone-walled room.
Something moves to your left, and you spin around to see a troll lumbering toward you, a wicked grin on his greenish-grey face.
You pull out your sword, but as you do so you begin to chant a spell. Concentrating, you send a wave of energy toward the troll which slams him into the wall. You follow up immediately with your sword.
The troll strikes back with his club, smacking your shoulder a nasty blow, but you manage to get in several good hits with your sword. The battle only lasts for a few minutes.
You search through the rest of the room, but find nothing of value. There is a nice pair of boots, but they look like the would fit the troll and are way too big for you.
You head back to the top of the stairs.