The stairs are made of stone and built into the side of the tower, winding their way down to the ground floor. You can tell that this is the ground floor, because you spot the door leading outside. It is barred by large chunks of fallen wall - it'll take a long time to get the door unbarred, and there's no guarantee that shifting the rubble won't bring more of it down on your heads.

You also spot an iron trapdoor on the floor, some pieces of smashed up furniture, and the bent and broken corpse of a kobold halfway buried in the collapse.