Clear the main talisman quest in Aquaria Towers and head above the main area to the open seas where Hunter and his Manta Ray are. Surrounding this field are invisible walls that stop you from leaving. However, if you dash against them with your head on the ground (you'll be moving slowly since all of your momentum is put towards the ground), you can slowly push through the barriers until you break free of the area.
Once you're free, you can swim all around the level and beyond it. Be careful - some walls are invisible, and once you swim through them, you won't be able to return to the void without performing the glitch again. Also, if you swim too far down, you'll fall out the water and land as if you're on top of a body of water. This space is a trap, though - if you touch a surface without water texture or dive under the surface, you'll die.
Submitted by: Artemis251