We moved to Seattle last year, and about 75% of my RPG collection went into storage when we got here. Shelf space went way down in the new place, so only about 250 gaming books made the cut to stay out and accessible.
Two of those were GURPS books, and I don’t even play GURPS — they made the cut because they’re two of the best gaming books I’ve ever read, full stop: GURPS Warehouse 23 (paid link), by S. John Ross, and GURPS Illuminati (paid link), by Nigel D. Findley.
I rate both of these books a 10/10. I’ve read the shit out of them (just look at that cover wear!), and hauled them around the country on multiple moves, and they’ve been a well of gaming inspiration for years.
GURPS Warehouse 23
You know the warehouse at the end of Raiders of the Lost Ark? This is that warehouse.
Warehouse 23 postulates that magic, conspiracies, secret societies, space aliens, weird science, and cryptids are real, and that the government keeps as much of the related stuff as possible locked away in the titular warehouse. So one thing this book is, is that: a marvelous sourcebook of all that great stuff, each thing with its own write-up. And as that, it’s excellent.
But you could build an entire campaign around the warehouse. Where there’s a conspiracy (or conspiracies), there are secret masters; you can fight them. Or join them! Someone’s got to acquire all of those Secrets Humankind Was Not Meant to Know, after all.
Warehouse 23 also walks you through lots of possibilities for who owns the joint, how Illuminated your setting could be (and how that impacts the warehouse), and what all that means to a potential campaign. Those lenses make the warehouse malleable, and Ross excels at making all of its possible incarnations eminently gameable.
Back to the stuff, though — this isn’t just a fancy equipment book. That would be dull. It’s a book of stuff which makes that stuff matter.
Take the Ark of the Covenant, for example. It gets a half-page of history and legends, a half-page on the Grail Order, a half-page on its rumored powers, and a half-page on questing for it and how to use it in different ways — combine it with other artifacts in the book, twist it sideways and make it not a physical artifact at all, etc. The two-page entry for the grail could be teased into a campaign seed in its own right, and that’s just one of the dozens of artifacts in the book.
Context is king, and the context around all of the weird and wonderful goodies in the warehouse is what makes this such a treasure trove of ideas. A world where all of this stuff — much of which is insanely dangerous and/or world-altering — would be an amazing gaming setting.
Which brings us to GURPS Illuminati.
GURPS Illuminati takes the core idea that there exists a world-spanning conspiracy — the Illuminati — and bends the whole modern world around it. It’s the default setting for Warehouse 23, but each book works just fine without the other.
Like Warehouse, and in the best GURPS fashion, Illuminati is bursting with ideas — all clearly and engagingly presented — which can fuel conspiracy-driven games in any system. It’s laced wth dark humor — like the list of 50 Awful Things About the Illuminati, which opens with this gem:
Everything here is true, even the false things
From there, you get an element-by-element guide to running this sort of campaign: character types that work well, ways to build the power structure of your conspiracy of choice, mapping the web of lies, adjusting for other genres, and on and on. The amount of good stuff packed in here belies the book’s relatively modest size.
Need secret societies? They’re in here. Need potential allies for foes of the Illuminati (likely the PCs)? Yep, they’re in here too. Oddball sidebars about conspiracies within conspiracies? Yeppers. A whole section on how to introduce the Illuminati, and the true extent of their world-dominating evil, to as-yet-not-paranoid-enough PCs? You bet.
And like Warehouse 23, it’s wonderfully weird. I get ideas from every page, and I’ve returned to Illuminati many times over the years — often just to read for pleasure, but also to stir up my imagination for various games.
I consider GURPS Illuminati an essential toolkit for running any game that even dabbles in conspiracies, and doubly so for one set in the modern world. Use it whole cloth, mine it for parts, blend it with other stuff — it’ll support you no matter how you want to employ it.
Like peanut butter and tinfoil hats
 As an aside, S. John Ross has a fantastic list of personal GURPS book ratings (one number for reading enjoyment, one for play); you can also see just the best ones. Plus the big list of RPG plots. And Risus (which I’ve gushed about on Yore). His entire site is basically a rabbit hole full of joyful exuberance — which, in a lot of ways, is what I want Yore to be.
 I’d forgotten that Teenage Martin decided, for reasons long forgotten, to use the front cover of GURPS Illuminati for target practice. I’m not sure if those are BB holes or stab wounds from testing out homemade Wolverine claws, but both options are about equally likely.