It's a sad fact that I don't get to run many RPGs these days (though I'm prepping for a return to the Fading Suns campaign and for my series of Pulp Hero adventures).
Instead, I browse through many RPG books and documents that I've accumulated over the years. There are a lot of systems and setting, a lot of layouts and images that instruct or confuse or enlighten.
I've learned about the effects of radiation and the timelines of the 1920s through the 1940s. I've read about various scientific superstructures like Ringworlds and Beanstalks and Dyson Spheres. I've slogged through theories on magic, the supernatural and the preternatural.
I've also exercised my imagination trying to image the light patterns against the face of a dark-skinned tattooed alien watching a space-battle outside the viewports of a starfrigate, a twin sunrise on a crystalline sea, and the view of the arching Ringword above me.
It may not be playing, but it relaxes, entertains and educates.