Riven came on multiple CDs. When you moved from area to area you had to swap the discs in your PC. I got part way through the game and it said "Please insert disc 5". I couldn't see any disc 5 and wondered if this was some kind of clever, 4th wall breaking puzzle.
Well, turns out the jewel case would open up an extra door and the 5th disc was there. It wasn't supposed to be a puzzle, it was just unexpected...
Certainly the 5 CD release was itself a stumbling block. It penalized exploring the island freely, which has some bad gameplay effects. When you're stuck on a puzzle in a Disc 2 area, should you keep exploring that area, or is it possible the clue you need is on some other disc? Which one? Are you willing to put up with the hassle? It wouldn't be so bad if each area was obviously self-contained, as they were in Myst, but in Riven they tried to change from a collection of puzzle boxes into a real world where the "puzzles" were diegetic. So there aren't really discrete "areas" anymore, or even puzzle themes restricted to an area. The clue you need may well be anywhere, which in combination with the disc swapping, makes finding clues into a huge chore instead of a delightful exploration.
And the biggest shame is it was built on very crappy technology (Quicktime) that even back in the day was held together with spit and string. For the better part of two decades, it was basically unplayable on any modern PC without major effort. So I haven't gone back to replay it since the original 5-disc release in the 90s. They did a re-release a year or two ago, which I guess is probably worth a shot, but my memories of Riven are just so soured by my experience. Meanwhile Myst holds a special place as a fun, quick little puzzle game.
Nowadays, though, the game runs fine in ScummVM. It's amazing how many games they've saved over the years. Myst III runs in a similar project called ResidualVM.
FWIW, if tech issues stopped you from playing Riven in the 90s, I really can't suggest giving it another try enough. If you get the ScummVM version, it's very likely going to work better on modern hardware (and, for that matter, doesn't require any discs). It's similar to Myst, but a much more artistically ambitious project.
Which is kind of funny, because the dev team between Myst to Riven was one of the transitions where they kept the team+tools the most similar between releases. (Myst 3 and Myst 4 had entirely different studios, with entirely different teams, tooling, and engines)
The next closest similar transition would probably be the Uru series to Myst 5 (but for wildly different reasons)
https://news.ycombinator.com/item?id=16801801
Assuming you must've gotten it after release because as far as my memory serves, the original Riven came in little brown sleeves clearly labeled 1 to 5.
I don't think your jewel case issue was an easter egg/trick. Just an attempt to fit 5 discs into 2 jewel cases.
Mine looked like this: https://imgur.com/LDkdx1k
Perhaps it wasn't the original release. Perhaps it was a regional difference. I agree, I don't think the case was intentionally made to deceive.