If you really want a challenge try Genius the Transgression. It's a fan-made expansion for World of Darkness. The world appears to have been optimized by a reasonably good rationalist to be as hard for an in universe character to analyze using the scientific method as possible, while still being an ordered universe.
Genius has it's far share of flaws. I don't like it.
I've been enjoying reading Less Wrong fanfiction, and I wanted to suggest another fandom that should have at least one rationalist fanfiction: Mage: The Awakening. It's a roleplaying game about "modern sorcery." My description can't really do it justice...