It is not wholly uncommon for those who use magic to carve out distinct, separate Demiplanes themselves, and perhaps even affix those spaces to objects. These spatial distortions are themselves Demiplanes – and often do not have constraints such as time or vacuum in them; they may also not have air and space.
On occasion, a Dimensional Rifts will open. Druids are very handy to have around because some of them have learned the skill of weaving the Fabric of the Veil back together, often using a bit of themselves in the process.
Dimensional rifts allow people to cross willy-nilly, and while this sounds charming and all, it also means that those from the other dimensions can cross over to here, and they are not often friendly. Indeed, they are three times more likely to be unfriendly or upset at encountering a rift – especially if they get trapped on this side of it.