Trivia: When the pygmies fall into the river after they blow up the bridge, look closely. As the right hand end falls into the ravine, one end is glowing from the blast, and one of the pygmies climbs on top of it and rides it down, hand waving, exactly like the scene from "Dr. Strangelove, or How I learned to stop worrying and love the bomb". Must be deliberate, and definitely worth a look.
Trivia: This is mentioned on the commentary, but I've got to mention it here because it's great. The scene where Rick's stalking Imhotep and there's a sequence of shots alternating pitch black and Rick's face illuminated, was quite tricky. They set up the camera on a dolly track, shut off all the lights, then tracked backwards while Brendan Fraser walked forwards, with two guys lighting the scene by using flamethrowers either side of the camera, trying not to fall down the holes in the floor of the set all the time. Genius.
Trivia: Brendan Fraser was somewhat amused and annoyed by the fact that the O'Connells owned a giant estate in the film, as he felt they'd feel more at home in an apartment or smaller house. Director Stephen Sommers said that the reason for the large house was because a large-scale action set-piece takes place in their home, and it just wouldn't work with a smaller house or apartment.
Trivia: Originally, Jonathan was going to own a casino, which he purchased with his share of the treasure from the first film. The battle in which Evelyn is kidnapped was going to take place there. However, for budgetary reasons, this idea was dropped early on, since it would have been a massive cost to build a casino set for only one or two short scenes. The battle was then relocated to Rick and Evelyn's house.
Trivia: At Izzy's home, there's a man in a bathtub reading a newspaper that's focused on in one shot. You can faintly hear him humming a few notes. The humming was actually done by director Stephen Sommers in an audible cameo, and it was looped over the scene. (Though contrary to popular belief, the man in the tub was just an extra - not director Sommers).
Trivia: One of the film's most common criticisms is that the CGI for the Scorpion King is notably of a lower quality than all of the other effects. There's actually a reason for this. The character was an early attempt at attempting to make a photorealistic humanoid, and thus the effect took much more work to complete. Additionally, the effect was made before a technique called "subsurface scattering" became prevalent, thus causing the plastic-like sheen on the skin. (Subsurface scattering is a technique that simulates how light penetrates and/or reflects off multi-layered surfaces like skin, thus allowing more realistic lighting and a less plasticy look.) It was so complicated trying to get the character to look "right," that they simply ran out of time and had to use what they had done, even though it wasn't quite complete.
Trivia: As of 2020, "The Mummy Returns" is still the highest grossing Universal "Mummy" movie both domestically and worldwide. It was the highest grossing of the Stephen Sommers series, and also grossed more than the 2017 reboot in unadjusted dollars. (And if you adjust for inflation, it actually grossed nearly twice what the 2017 film did).