One could have a gun cabinet set into the wall. There are lots of gun cabinets five to six feet tall and almost as wide that are a strong as a safe. But, calling a wall safe is a little miss leading. I was thinking like a 2 x 2 x 2 box. A small nuke would be fun, but as it has been said, a little over the top. But, we have zombies running 50miles per hour...