Well David, I used what I had to my best advantage. There's a corner of my basement that provides me with a standard sized closet with block on three sides, the corner of the basement and the wall of the chimney. Over that I bolted and welded steel plates and custom made a door using steel pipes as locking bolts. The mechanism isn't something I want to make public knowledge but know that I dont' use a key or keypad for locking.
Without some serious welding equiment and lots of time, no one is getting into this sucker without my say so...
If you have access to large sheets of steel and welding equipment, it only takes time and ingenuity.