The first thing that bothers me is that most “bunker” plans are built with the same three‑layered wall concept and then stop there. Mutants don’t care about layers, they care about any weak point. Start with a 12‑inch reinforced concrete wall, but embed a steel lattice that’s interlocked with a 4‑inch steel plate on the interior side. That gives you the mass to stop a brute, and the lattice to absorb kinetic blasts. The entryway should be a vestibule with three successive doors. The outer door is a steel blast door with a hydraulic lock that closes automatically when a pressure sensor detects a sudden increase in pressure—think a blast from a mutant charging. The middle door is a small chamber with a gas‑scrubbing system, so if the mutant tries to poison you with spores, the air will be cleaned before it reaches the inner door. The inner door is the “real” barrier, a heavy steel plate that can be locked with a combination lock tied to a biometric scanner. If you’re still feeling cautious, mount an infrared sensor that triggers a loud alarm if someone tries to pry open the inner door while the outer doors are still open. Ventilation is often overlooked. Install a redundant system: a primary HVAC with a high‑efficiency particulate air filter, and a secondary, battery‑powered backup that can run for at least 72 hours. Make sure the ductwork runs in a zig‑zag pattern so that if a mutant cuts one section, the airflow is interrupted and the filter doesn’t just get saturated. Finally, add a small, hidden “panic room” behind a false wall. It should be a small, one‑person space with a manual override for the main doors and a backup power supply. If the mutants break the outer doors, you still have a place to hide and a way to call for help. If you’re going to build something for a horde, don’t just stack bricks. Think about every possible angle, and then think about how that angle might be exploited. And remember, the easiest bunker is usually the most vulnerable.

You’re right, the corners are the Achilles’ heel of any concrete shell. I’d suggest a double‑layer approach: first, embed a rebar cage that’s angled at 45 degrees across each corner so that a blow can’t simply pry the two sides apart. Then wrap that with a thin sheet of high‑strength composite—think aramid fiber, not just steel mesh. Cement and epoxy will bond well to that, but make sure the epoxy has a low elastic modulus; you want it to flex enough to absorb a claw strike, then snap back into place. The quick‑release bolt is a neat fail‑safe, but you should lock it in a recessed slot so the mutant can’t jam it with a claw or a pincer. And instead of a lock‑pick kit, which is a hassle in a panic situation, install a manual override lever that disengages both the blast lock and the biometric lock simultaneously. Just pull the lever—no fiddling, no chance of a glitch. The biometric should have a secondary “thermal override” that kicks in if the body heat falls below a threshold, but that should be hidden behind the lever so you don’t need to think about it. And a quick note on simplicity: keep the sensor circuitry as minimal as possible. One pressure sensor per door, one temperature sensor for the biometric, and a single microcontroller that runs a deterministic watchdog loop. Anything else just adds another point of failure. That way, you have a robust, yet uncomplicated defense against the mutants.