All-Star Cast: Paul Newman, Steve McQueen, Fred Astaire, Faye Dunaway (before her wire hanger days), William Holden and OJ Simpson. Jennifer Jones was borderline, as she had been a star during the 40s and 50s, and this was one of her last films before retiring completely.
In a scene where a bunch of people are fighting to get onto an elevator, the extras were really fighting to keep off the elevator, since anyone who did get on it was pretty much done, and anyone who stayed off it was guaranteed a job for the next couple of months.
In the scenic elevator scene, the explosions were bigger than the actors were anticipating, so they really were panicking.
The director fired a handgun into the air to get a genuine look of surprise from the actors' faces.
Life Imitates Art: A real fire broke out on set, and Steve McQueen found himself briefly helping out real firefighters. One of them didn't recognise him and said "my wife isn't going to believe this", to which Steve responded "neither's mine."
The pink satin cape worn by the mayor's wife was part of a costume worn by Jean Simmons in Desiree.
The large sculpture in the Promenade Room was used in Hello, Dolly!.
Real-Life Relative: Paul Newman's son Scott stars as a fireman. This is the only film they did together.
Reality Subtext: Fred Astaire was genuinely terrified during the explosions, so his look of fright is real.
Science Marches On: Since the making of this film, there was the notorious MGM Grand Hotel fire when it was discovered and publicized once and for all that in a major structure fire, it's not the flames themselves that is the major killer, it's the smoke.
Significant Anagram: Meta. "The Towering Inferno", as is often noted, is an anagram of "not worth fire engine".
Wag the Director: Steve McQueen, a veteran of this trope by then, requested that he and Paul Newman have the exact same amount of lines in the film. Also he insisted that he not appear until forty three minutes in, by which point Newman would have used up a lot of his lines. William Holden attempted to - demanding he be billed first. But as he'd been in a few flops lately, he gets third billing.