Rifts

Unlike gorges, rifts are not formed by erosion. Rather, they are the scars of tremendous upheavals deep in the earth. Rifts are places where vast blocks of stone rose, sunk, or slid past one another in long-ago cataclysms, leaving tremendous chasms. Rifts may be dozens or even hundreds of miles in length, and sometimes miles deep, but they are rarely very wide-most are less than a bowshot across.

Rifts sometimes break apart preexisting features such as cave systems, presenting formidable obstacles to creatures traveling through caves. In order to continue when faced with a rift, the traveler must climb or descend to the appropriate level on the far side. Like gorges, rifts often serve as vertical highways in the Underdark, offering travelers the opportunity to change depth with little fuss.