Gates of Night

The Gates of Night are believed to be the only portal through the Walls of Aaroth. They are commonly depicted in art as enormous doors, or a portcullis, or other awesome, divine, physical portal. Some believe the gates are merely metaphorical for some sort of arcane, divine, or other metaphysical passage. They are a topic of ongoing debate among and between sages, priests, mages, and philosophers.
Some elves who survived the Riddic-sûr-Danith Or, and who witnessed Baugoth's defeat, claim they saw actual Gates manifest in the heavens as the Dark God hurtled through them.
Astral travel appears to provide some sort of tunnel through the Gates of Night and the Void beyond, permitting passage between the Inner Planes and the Astral Plane. This, too, has produced ongoing speculation and debate among the learned.