Wow, nice! I really dig puzzles in impossible maps, and this one is amazing! Are you using the new Godot portals or it's a hand-made implementation? Good job anyway!
Thank you! This is done with Viewports and shader materials (mapping a
SCREEN_UV). Do you have a link to any information about the new portals? I’ve ran into some issues with my approach due to difficulties with implementing efficient culling or timely updating viewports.