Mind Palace

A Mind Palace is an ethereal void inside the minds of most living creatures, that can be accessed via certain PokéPowers.

Those with PokéPowers seem to have more habitable Mind Palaces, even allowing others to visit them either by invitation, or force.

Mind Palaces are able to display memories of a person (as seen in Andros' Mind Palace), as well as reflect their current emotional state.

They are often depicted as black oily voids, populated by occasional items of furniture conjured by the owner of the Mind Palace.

Kenny's Mind Palace
The most featured Mind Palace is that of co-protagonist, Kenny. Kenny's Mind Palace houses Pete and Tookey, Kenny's spirit guides, as well as a single chair.

Much is mysterious about Kenny's Mind Palace, and he seems to be discovering new things about it each time he visits.