So what do you think? How do you run it? Is your campaign setting realized and existing even without character interaction? Or do you only detail what the characters are interested in?
I...don't really do either one?
We play to find out what happens--but I also do prep work. A fair amount of prep work, actually. I try to give enough weight, enough significance to things so that there is the feeling that
yes, the world
really does exist beyond the limits of what the players directly interact with. I try to have at least
some prepared thoughts,
some underlying connections. I don't really know how, for example, you can have a true mystery (e.g., something where there's a definite "whodunnit" but you have to piece together the clues) without preparing to at least some degree the answer to questions like, well, "who done it?" But that doesn't mean that the path is fixed, nor that one cannot discover new information which casts the old in a new light.
For example, a while back the party was tracking down a woman who had been married to several different spouses, each of whom had died, with just enough justification to throw off suspicion (e.g. one died of injuries from combat, another of illness, one was murdered by someone else, etc.) The party already had their reasons for tracking this woman down, it would take too long to explain why, suffice it to say they were committed to ending her. But as they delved deeper, they began to realize (read: we as a group discovered) that things weren't as they seemed. Far from being a conniving manipulator, she seemed
genuinely unaware of her connection to anything nefarious. The players dug deeper and discovered, to their horror, that in a very real sense the woman
was unaware: the pact she had made with her succubus patron (matron?), due to her failing health as a teenager, was powered by
grief. So each time, the succubus removed any memories she had of the pact and other such things, so that
the grief at the death of her spouse would always be real. Needless to say, the party completely changed their goals at that point, and decided to try to find a way to break this lady out of the cycle she was trapped in, rather than kill her to complete the contract they were fulfilling.
And all of this came about because the party Druid signed a contract with a devil. I did a fair amount of work (as I've said many times here) to make my devils interesting and not complete idiots, and that information is stuff the party only learned during the process of working through this situation. Is that "realized and existing even without character interaction"? Is that "only detail[ing] what the characters are interested in"? Is it both? Neither?