Shadowgate

From Glen Cook Wiki

A magical portal in the far south which leads to the Glittering Plain. The Plateau is a kind of crossroads leading to Shadowgates in sixteen worlds, all geographically identical to the "real" world (apart from some differences in the stars and moons). The Shadowgate cannot be passed without an appropriate key, of which the Lance of Passion is one. It is primarily an invisible, magical construct, although in days past a physical stone arch was built to correspond to the magical one. It is wide enough for four people to march through abreast.

The Shadowgate to the world of the Black Company was damaged by the Shadowmasters; they repaired it clumsily, with Longshadow weaving his true name into the gate. There are "cracks" or pinholes through which Shadows can leak.

Shadowgates are vulnerable to sorcery; the Voroshk accidentally destroy their own, leaving no barrier between their world and the Plateau. However, the gates are maintained by Shivetya and repaired when he sees fit.