Feywaters/Feyshores and all the other things they get called, normally exist as “pockets”, a wrinkle in the cloth of reality. A fey cave might be much, much larger on the inside than the hill in which it supposedly exists. They are generally accessed through a specific entry point, that is very difficult to find or even invisible. A group of fey islands might only be visible when approached from a certain heading. Some pockets may be accessible by different doorways that are leagues apart, or only accessible at certain times, or when carrying a particular herb. The ‘key’ might be anything.
A doorway into a fey realm can be identified by an arcana check. Fey races get a bonus.
Fey realms appear as exaggerated and enchanted reflections of the sunlit world. Trees will appear gigantic and ancient; caves are full of odd formations and weird glowing motes. Strange occurrences and effects are common. They are mutable, and easily shaped by powerful magic. Magic Rituals take less time to cast and are more effective in fey realms.
While such places exist as discrete pockets, some powerful fey claim to know how to travel between them without going via the mortal world. This involves travelling through even more dangerous and magical landscapes/seascapes, that become more and more unpredictable until they completely break down into the Elemental Tempest.
Some isolated pockets of the fey world become stagnant and imbued with dark energies. Such ‘Shadowfells’ reflect the presence of death, both natural and unnatural. They might be swamps, or deserts of black sand, or stranger landscapes. Evil spirits inhabit these domains – darkly twisted fey creatures, beings of shadow, undead and demons.
Most fey travel, if they need to, from pocket to pocket on certain dates in the dead of night, while all good mortals are sleeping. Invisible ‘leylines’ (also called fairy trails or dragon paths) often follow the routes taken.