Worlds within crystals or pocket dimensions are most often referred to as Luumakheder, or simply kheder. Examples of small Luumara can be seen in many spells and magic items. Such as the space created by the spell Rope Trick. On occasion kheder are used to facilitate a transference of the consciousness’s information to a true Luumara such as the Dread Forest. Since obtaining a new direct Tether to a Luumara is more difficult than finding something already Tethered this is the most common way to travel to and from them.
Sometimes storage devices that utilize Fractalmancy are mistaken for gateways to kheder such as Gorb’s box of trinkets and bags of holding.