If you have obtained this yourself on the quest, you can use the Hoist on the second and third floor. You can also change the destination of the second floor's hoist by using the lever by it.
.... the lever points to the left, the hoist will bring you one level higher. If it points to the right you will go one level deeper.
These are the construction plans of the hoist. You now understand the mechanism and can use it according to your wishes.