One of the things I always tell people is that I'm very "detail-oriented."
For my fiction, this means that I research things almost constantly. I have a "Russian"* character in CALLARION AT NIGHT, so I looked up Russian speech patterns; recently I found a resource on writing the Irish accent without using dialect (needed for another character). I have books on architecture, weapons, Nazi thought, numerous printouts of baby names from various cultures, etc.
I also know the exact mph of a horse at a walk, trot, canter, and gallop -- information I used to calculate the distance between the cities of Haldor (the world of SON OF MAGIC). And did you know that the average person's walking speed is 2 to 3 miles per hour? That's another random tidbit of information you can use to calculate distance.
All of this translates (I hope) into stories with as few holes in the background as possible. I'm not a fan of the practice of "making it up" if you don't know it. Mostly because there's always someone out there who's going to call you on any bit of information you get wrong, no matter how small. This is why writing historical fiction is so hard. You have to get things dead-on accurate for your period or else the story doesn't work.
Same goes for any part of a fantasy/sci-fi story where you pull something from reality. It has to be accurate or it doesn't ring as factual, with the end result being you lost the reader. Probably the worst thing that can happen to a storyteller.
So, dear readers, I told you some of the research I've gathered. Now it's your turn. What's the weirdest tidbit you've ever had to look up for a story?
* The character isn't Russian per se, but he's from a country that's heavily based on Russia.