Astral Planes

Vorago the Whirlpool has consistent but one-way connections to the astral sea and astral planes. Gods can exert influence, devils can tempt peoples' dreams, and warlocks can receive pact power from extraplanar patrons. All of the D&D astral planes, including the Nine Hells, Elysium, The Abyss, and Limbo are contactable from Vorago (if you're clever).
Leaving is much trickier though: Rituals and devices that typically create a portal do sometimes work, but the portals are bouncy, viscous, or electrifying in one direction, though they work extra well the other direction. Spells that directly shift you to a plane can't harmonize for long enough, astral tuning forks lose their note, etc. There's no feywild or shadowfell to go to at all, in their cases. Teleportation within Vorago is usually fine, strangely.
Mundane objects and small magical items can sometimes be sent through a "direct line": incense or prayers to a god, a soul to a demon via a contract, or a very weak demon back to its home layer once killed.
Large planar creatures like angels, devils, demons, astral dreadnoughts, etc, cannot fully return home but maintain a connection to their plane / god and their magic. Their essences cannot escape to their home plane; they can be captured by enterprising mages to be reborn or consumed. If left alone, they will gradually disperse; the site of their death may become hallowed/tainted, as might the weapon that killed them, but they are dead.
A great archmage once put it as, "It's like a godsdamned lobster trap. Everything gets in, but only the small fish get out". Small fish, in this instance, is not referring only to size, but also magical investiture and even strength of spirit.

Type

Metaphysical, Astral