The Drawbridge is an obstacle that is encountered in the game.
On the near side of the Drawbridge there is a Lever that can be used to lower the Drawbridge.
It pays to have a look in the cave that is down inside the Chasm here. The upgrade to the Floating Platform that the Wizard can conjure will help a great deal, as the Thief can attach her Grapple Hook to it and then lower herself down into the Chasm.
Important note: when the Drawbridge has been lowered it is not possible to explore the Chasm here.
For a list of other types of obstacle see: Hazards