Foucault’s Pendulum by Umberto Eco is a fantastic novel for doing this. You find yourself sucked right into the conspiracy, only for him to then reveal the facts that destroy it.
There’s a subplot on how the number of letters in a document proves the Templars possession of the Holy Grail. A character then shows how a random shopping list follows a similar pattern.
One of the most memorable lines from the novel for me was something along the lines of "if you lend too much credence to symbolism, you end up believing the male penis is only there as a phallic symbol" (said by the main character's girlfriend, if I remember correctly).
It's also fun to read Umberto Eco's take on Dan Brown and his Da Vinci's Code. Eco was joking that he feels he should get some credit for the whole thing, as Dan Brown is so clearly just a character from Foucault's Pendulum.
The Illuminatus trilogy is pretty avant garde in style, whereas Foucault's Pendulum is fairly standard prose. Really depends on what type of book you want.
Yes, and Foucault's pendulum is very literary research oriented (long expositions of guys surfing their zettelkasten), where Dan Brown's books are standard pop fiction action fare.
Every 15 years or so, we get a new, more popularly approachable entry in the "Templars/Illuminati are real" mystery thriller genre. We're about due another one, but I'll bet I missed it because it's in the Young Adult Fiction section.
There’s a subplot on how the number of letters in a document proves the Templars possession of the Holy Grail. A character then shows how a random shopping list follows a similar pattern.