HAPPY ENDING
The only "correct" ending is to meet with Gehn, capture him in the trap book, free Catherine, then open the Star Fissure. Save your game just after solving the Fire Marble puzzle, then try these...

OTHER ENDINGS

1. Open the Star Fissure before visiting Gehn or Catherine.
2. Visit Gehn and capture him in the trap book and go back and open the Star Fissure \ without freeing Catherine.
3. Visit Gehn an do not capture him, and do not free Catherine, but go directly back and open the Star Fissure.
4. When Gehn holds the trap book up for you to go first, refuse to link. Return two more times and refuse both times.
5. After capturing Gehn in the trap book, touch it yourself.
6. After capturing Gehn in the trap book, return to the Moiety Age and touch it.
7. Touch the trap book when Keta gives it to you in the Moiety Age.
8. After Keta gives you the trap book, return to Riven and touch it before visiting Gehn.
9. Visit Gehn, then go to the Moiety Age and get the trap book. Touch the book before going back to Gehn.

Some players have put some thought into freeing Catherine, but not capturing Gehn. No one has been able to do this successfully though. Normally, you must trap Gehn to gain access outside the cage so you can find the combination to the lock at the elevator up to Catherines prison. Some have tried the brute force method of opening the lock, but it doesn't work. The game program sets the code only after Gehn becomes trapped in the book. Until then, no combination will work, so to free Catherine, you MUST trap Gehn first.

More Riven Stuff
Riven Illuminated * My favorite Riven site