1. Cary Elwes almost missed out on playing Westley because of Chernobyl.
In 1986, when director Rob Reiner and producer Andrew Scheinman were casting the movie, Elwes was in Berlin shooting Maschenka. The pair was (understandably) trepidatious about traveling to see him, given the uncertainty surrounding health risks in the aftermath of the Chernobyl disaster, since he was so close to the then-Ukranian SSR.
“I’m looking at maps and they have gray areas where the nuclear fallout is and I don’t like it,” Scheinman wrote in one of the book's many anecdotes offered by Elwes' supporting cast and crew. “Rob was like, ‘Don’t go if you don’t want to.’ But I did. I just remember running fast into the hotel, like that’s going to do anything, and literally leaving a thousand-dollar jacket behind. I didn’t have that much money and I certainly didn’t have any other jackets like that, but I couldn’t wear it anymore. I just left it.”
2. Elwes aced his audition thanks to Fat Albert.
3. Colin Firth and Danny DeVito were considered for roles.
In an alternate universe, The Princess Bride could have been directed by Robert Redford, who (along with Norman Jewison, John Boorman, and Francois Truffaut) tried and failed to get the film made. And it could've starred Colin Firth as Westley, Danny DeVito as Vizzini, Sting as Humperdinck, and Arnold Schwarzenegger as Fezzik. Each was considered for the film at one point during pre-production.
4. There was a last-minute costume change for The Man in Black.
The Man in Black's now-iconic scarf was not part of the initial design, but costume designer Phyllis Dalton sensed something was missing in the very first fitting. “She called over her assistant and asked her to fetch some black satin," Elwes wrote. "When the assistant returned with the material, Phyllis tied one piece around my head and another around my waist like a sash. ‘There, that’s better.'"
5. André the Giant had a nifty technique to memorize his dialogue.
6. Mandy Patinkin had a deep, personal connection with Inigo Montoya.
7. Bride shared some DNA with Star Wars.
8. Filming started with "a fairly simple scene" that was not at all simple.
9. Author William Goldman was literally praying for success on set.
10. Elwes upped Westley's heroic street cred.
Westley's headfirst dive into the quicksand was not how he was originally scripted to react — Elwes was supposed to step in and hold his nose, but felt that looked "feeble."
"There was something rather unheroic about jumping into quicksand feet-first," he wrote. "Especially holding one's nose." So, the actor suggested a headfirst dive — an idea that gave everyone pause. While the sandpit featured a trapdoor that gave way to a host of padding, if Elwes executed the dive wrong, he could have broken his neck.
Eventually the rejiggered leap was tested with a stuntman, who executed it perfectly, so Elwes was allowed to attempt the dive himself — and he nailed it. In fact, the scene you see in the finished film is actually the first take. "It definitely helped the movie," Scheinman wrote. "It's way more Errol Flynn-y and hero-y to dive than not to dive."