When i was a kid, we had a fallout shelter. It was not called a fallout shelter, it was called a "root cellar", but there was little difference,
looking back on it. It was dug with hand tools into a hillside, and the walls and ceiling were supported by heavy timbers that were bolted
together. Because of bears and other animals, a very heavy wooden door was built to access the cellar. We'd store vegetables from our garden and
some fruits in there bedded in straw, and that, along with canned goods my Mom put up and dried and smoked meats, would sustain us throughout the
winter.
Our neighbor had a root cellar made of rock and concrete, and it also kept produce from freezing throughout the winter. It wouldn't have been as
good of protection in the event of nuclear fallout, but far better than any wooden structure.
That was common for us country folk. A person living in the city might not be in as bad of shape as they might imagine. Suppose a person lived
in an apartment -- not on the top floor. They may be able to increase their survivability by covering the windows and doors with as much density
of material as they can. I think it's important to mention that in such a situation, the need for uncontaminated water might well quickly become
as or more pressing than the fallout itself.
To answer the question in the OP: No, we don't have an underground fallout shelter. We do have acess to a cave or two which are used during
hurricane times. These do not block or filter airflow, so their effectiveness as a fallout shelter would be somewhat questionable and dependent
upon the location of the strike, wind patterns, etc. We do keep 150 gallons of steralized water in three plastic barrells in addition to two
concrete cisterns.
Way back when, I lived in a city, and I felt vulnerable. That is when I began storing food and water. I had a friend who was my survivalist
mentor, and he kept a huge stack of otherwise useless phone books, for the purpose of fabricating a "desk shelter" in the event of fallout.
I think it's important to think about, and talk about with your family, even if you believe the probability of needing to respond to such a situation
is minimal. Escape routes from your home to ......? How to best shelter in place, if that is your only option. As others have mentioned,
printing, reading and understanding the fundamentals of building and using a Kearney Fallout Meter is a good thing to have under your belt. The
Ki4U website has a lot of good information.
Just in case, you know?