A player whose character is becoming a priest of portals asked how they could build a Well of Worlds.
I have guidelines for that (I finally remembered). Guidelines are also posted at the bottom of the post.
One needs a stone from each of the Portal Towns and arrange them in a circle. The well will need an element from 4 Elemental Planes. If it isn’t Earth, Air, Fire, Water as the 4, word is the Well will turn strange but others say it will be strange no matter what.
Add something from the Far Realms for spice (and distance). The Well will need a guardian bound to it so that nothing comes from the other side of it when planes are in alignment and boundaries are thin. Once you have that, you’ll have your Well of Worlds…