If you're brave enough for fly mode, there are a few other tricks that you can try by making some changes to the _init.dat files.  The basic approach is to open these files  -- game_init.dat, player_init.dat, win_init.dat -- and change the "data" that the program reads when it first loads.  Use Notepad or another text editor -- you want to keep them as text files.  Below are some of the tricks that people have discovered.

Author	Trick	File modification	Image
Marack	Gives a "drunkenness" to your navigation	Marack found this and the next trick by digging into the realMyst.exe file.  In the win_init.dat file, change FirstPersonDeadCenter to FirstPersondrunken
Marack	Creates a rainbow effect	This is pretty wild.  In the game_init.dat file, add the following two lines after Ambient Scale:      LODColor    1      LODAll    1
lonelyto25	Turn one animal into another	lonelyto25 gives instructions here.  At right are some bats as fish.
lonelyto25	Turn the player into an animal	lonelyto25 gives instructions  here (same link as above, second post).  The advantage of this trick is that it allows you to fly through many objects, which in turn gives you access to some otherwise unreachable places.  I give some examples here.  At right is an image from one of those places, the Selenitic fire pit.
lonelyto25 and Zardoz	"Visit" the Puzzle Age	By turning myself into a bat (see above), I was able to get right up to the Rime viewer, which is as close as we'll ever get to visiting this Age (or so it seems).  lonelyto25 created a saved game and a set of init files here that will get you right there.
Zardoz	Slow motion butterflies	This slows the butterflies way down (you could also do it with the bats).  In the game_init.dat file, change maxsp=0.5 to maxsp=0.005 (or similar small value) in the line ending with  beh=beh\butterfly\butterfly_fly.BEH).
lonelyto25	realMyst Warp Speed	Among the many intriguing references that you can find in the realMyst.exe file from the demo (discussed in this section) is "camfovmult".  lonelyto25 inserted this into the game_init.dat file for the real game (it also works for the demo) and got a warped look. To get this effect, insert           camfovmult          # in the game_init.dat file after the FOV line.  Substitute any number from 0 to 10 for the #.  Fasten your seat belts and start up the game.  The number 1 appears to produce a normal effect; above 1 gets the warped look; a 0 (or any decimal between 0 and 1) produces a telescopic effect (bottom picture) that will drive you nuts!