There’s a gap just above the lobby of the tower near the windows where you can jump down and then go up to reveal the empty shell of the tower between the lobby and the PixelTail offices.
(Edit) All of the windows on the front side of the building have gaps, but the one shown in the video is the only one you can squeeze through (I did not test the others with the tiny potion though). The sides of the building also have parts of the interior’s default-textured structure poking out (pictured). The back of the building appears to be completely fine.
