Nice!
I think having a fallout shelter would be a good idea, no argument. Groundwater is way too high here, at least to go underground.
Oh, the bottom half of the shelter is definitely below the water table here in Houston.
The whole room is intact and maintains its integrity, and thus floats a little. There is a rectangular outline in my lawn indicating that the entire structure has raised a few inches over time.
I was advised to keep it full of water to prevent that.
It was wired for electricity, and one of the ways I dated the structure was by dating the incandescent light bulb that was still in its fixture. In the old days, round incandescent bulbs had a small bump at the very top. It was not completely spherical.
Thus, my guess is that it was installed during or shortly after the Cuban Missile Crisis.