Sans will have a mind palace located in his room. It will look exactly like the door to his room in the game, complete with mysterious lights flickering from the bottom. The door is locked with several bolts and is inaccessible from any other angle. It'll be extremely difficult for anyone to get in, but anyone who does will find a pretty strange place inside. It'll basically be a huge black void with sort of "islands" of reality, each one modeled after certain locations that are important to Sans back home. Sans himself will be virtually impossible to find as he's very deep in the void, standing in front of a huge translucent barrier with a broken hole in it. Beyond the barrier is a lot of colorful light that looks super inviting, but can't actually be accessed.

Sans's mind will be loaded with defenses as he tries to keep people out. Everything from bone constructs to creepy, pale faces in the dark will confront any intruders in an effort to drive them away. His goal will be to essentially just shove intruders back out the door, since he doesn't want to actually hurt anyone.

Rick won't be getting a palace but he'll be exploring other people's and probably trying to set them on fire.