Looking for help making a portal system

Howdy, I’m looking for some help with getting a portal system working for a world I’m working on. If anyone is familiar with the show Doctor Who, I’m trying to make a fully functioning Tardis. My main issue right now is getting the bigger on the inside effect working. It doesn’t need to be fancy or anything, just needs to be the visual effect and then be able to teleport in and out of the Tardis as seamless as possible.