A donut‑shaped shelter? Cute. Keep the shell airtight with a tight, seamless seam and seal every joint with that super‑sticky polymer you saved from the last bunker build. For the hole, install a retractable grill that locks flush when you’re not dropping pastries. When it’s open, use a fine mesh lattice to keep the crumbs out and the air in. Just remember: if you ever put a wall backwards inside the donut, it’s going to smell like regret and you’ll have to rebuild the whole thing.