I recall a sci-fi story, likely a short story in a compendium, set in the future where portals are used to move about as the outside is believed to be uninhabitable due to fallout from a war. The portals are referred to as Doors with the emphasis on the capital 'D'. A child finds and uses a door, i.e. a physical opening doorway that leads outside and find the outside is pleasant.
Can anyone identify the story or even better, the book?