This is a glitch in Super Mario 64 DS that, as the title implies, creates an Unloaded Town and other Glitchiness. To do this, go to Wet-Dry World at the lowest water level. Then, go up to the third level (the level below the one with the Chuckya). There will be a large metal box in front of you. Push it into the left corner, and jump on it. Go into that corner, facing the back wall. Go into 1st person view mode (press X twice), and rotate the camera to the left. Right after the camera goes behind the left wall, press X again. You will fall through the box. Now, walk into the aforementioned corner (the one you were just standing in), and you will go through! Make sure to move in mid-air, or you will fall out of bounds and die. Depending on where you moved, one of two things will happen.