RAF Holmpton in East Yorkshire.
Like many, it is disguised as a 1950s type bungalow which is actually the entrance.
It opened up to the public as a museum a year ago and I was one of the first ones down.
Several flights of stairs, corridor followed by a very long corridor that descends to the blast doors.
It was fascinating inside! Various rooms over two levels still equipped and resourced ready for a nuclear war. Bunk beds were still in place and even the cups and saucers!
The 'command' room was by far the most interesting - lit up displays, war paraphernalia and even an actual bomb (not loaded!) that we sat on (think movie Armageddon!)
Easily spent 2 hours down their and so many museum officials who worked the bunker on hand for informal guided tours, questions etc.
We went as a group and even my then 4 year old was intrigued.
They did say that once the bunker was built, it wouldn't actually withstand the nuclear blasts of the day, and certainly not now, and doesn't help that the generator is in a building outside.
Still, if I am nearby, I would fancy my chances bunking up in it until major dangers had passed.
The most bizarre thing was they had a resident cat and all doors (I think except the blast door) had a cat flap!