Or perhaps it's a rainy day and you can't play outside, but you'd still like to have an adventure.
Or maybe you need to research a particular topic related to life in the 20th century.
Then I recommend spending a few minutes (or a few hours) with the Google Books online archives of Popular Science and/or Popular Mechanics magazines. I find old back issues of these magazines at estate sales from time to time, but the digital version of an old magazine gives us a chance to read the stories and see the pictures without worrying about damaging the old paper.
For the lover of interesting old things, these websites are treasure troves.
Here's the link to all the archives for Popular Science:
And here's the link Popular Mechanics.