Say there is a nuclear explosion in the downtown of my US city.
If it’s that close you then essentially you’ll need to decide whether to die quick or slow :/
If you’re actually planning on surviving you’d need to stay in an underground bunker or something similar for at least 3-5 weeks to be safe enough to travel outside (and we’re assuming you have clean sources of food/water, bathroom, etc, during that time). If you make it that far then afterwards you’d likely want to go outside & get as far away from the radiation zone as possible.
Coincidentally the basement of my work building actually has a fallout shelter sign from back in the day so the basement might survive a blast but I don’t see how I’d make it 3-5 weeks without being extra prepared for that beforehand.