The Bridge is a rather small red covered bridge in the town of Winter River on the way to the Maitland Residence. It becomes a major player in the deaths of Adam and Barbara as Adam swerves out of the way of a dog and accidentally crashes through the side of the bridge and into the river below. Had the bridge not been there the Maitlands could have easily survived the crash (being killed, to be exact).
Later, Lydia references the bridge in a suicide note she writes