Overview
Like a hole going through a folded piece of paper parallel to the 2 dimensions the paper takes up, wormholes go through space parallel to the 3rd dimension. This space pilots go through when going between wormholes is colloquially known as Plane Four. Rings of mirror images of the destination line the 'walls' that pilots see when going between wormholes due to light going in circles, similar to how black holes have more than 1 Einstein ring if you look close to the edge of their horizon. Due to the gravitational forces experienced inside active wormholes, you are forced to go the direction that you came in going, however sometimes wormholes collapse during transit. This leads to your ship floating in a theoretically black void where there is nothing around other than the stuff that came with you. This cannot be tested as it is impossible to go up and down in the 4th dimension after dropping out of the wormhole.
An experimental technology is in the works, which could allow a 3D being to traverse 4D space by changing which slice of space they are viewing .