There are other planes. One of them is Faerieland.
Travel to other planes is (almost) not accomplished with portals and teleportation spells. (While wizards cultivate that mythos, they aren't capable of half the things that people think they are.)
Instead, planar travel is accomplished by. . . doing stuff.
Faerieland can be reached by anyone who ever gets lost in a forest.
They must be completely lost. Confounded. Muddled. They must be completely without a way to retrace their steps. Even a wizard, who has a spell prepared to find their way back, cannot find their way back, no matter how drunk they get.
Oh yes, drunkenness is a common strategy among those who want to reach faerieland. Very common. (Unfortunately common, as owlbears will to terrible things to a drunk party.)
Children stumble into faerieland all the time. They rarely stumble back.
Clerics rarely find faerieland, since their footsteps are guided by their deity, at least in part.
Unless everyone is lost, no one will find faerieland. (This is why no army has, or ever will, find faerieland.)
Supposedly, returning from faerieland occurs only with the permission and abilities of the faerie queen. (But there are many other rumors.)
The Thin Cities are reached by going down an ocean whirlpool during a storm. This usually works, if the storm is big enough.
Orzelle is reached by walking a certain pattern within the Labyrinth of Condora. The people are then transported to a similar labyrinth in Orzelle.
The Hollows of Teragaius are reached by getting lost while underground.
The Plane of Air* is reached by reaching terminal velocity while painted yellow.
There's also a plane that can be reached by a well-known ceremony involving tiny obsidian pyramids, a fat woman, and three rabid weasels inside a cauldron. No one's ever come back from this plane, but speculation is rampant.
There's also a plane that only Naus-garaunts can reach.
*No other elemental planes are known. Scholars even debate of there is such a thing as an elemental plane. Wizards are confident about it, however.