how do I get the bonus dungeons? (DoS)

I beat ffI, but did'nt get soul of chaos, do I have to beat both 1 & 2 to get it?

The Soul of Chaos dungeons are all accessible via FFI's world map. The only requirement for getting inside them is defeating the corresponding Chaos. You need to beat Lich to get inside the Earthgift Shrine, beat Marilith to get into the Hellfire Chasm, beat Kraken to get inside the Lifespring Grotto, and beat Tiamat to get inside the Whisperwind Cove.

I have no idea how you completely missed them. You even get a little cinema of one being unlocked after beating each Chaos.

Just explore the world map and you will see caves lying around which you never been before. Or even much obvious, a whirlpool in the middle of nowhere.

theres one inthat whirlpool one near the volcano one near the chaos shrine and one in those islands where you can upgrade characters.

Those were part of the soul of chaos> I just thought those were random bonuses that opened after each crystal was obtained.

Anyways, what about in ffII? I'm just about done with that too.

FFII, I believe, when you finish a game, you have to play as the dead characters in a subplot. I haven't finished FFII yet, that is just what I have heard.

Yes Minwu is the main and you battle though a almost alternate reality. Yeah Josef vs. Borghen! and Richard vs. Worm! You will play through M. tower, the dragoon cave, Paft, and the ever annoying Jade Psaage whih is ironic being it was a gateway to HELL!

Actually you don't have to go through the Mysidian Tower again, it's a completely optional quest and it's only the top floor of the tower with no random encounters. Just Ultima Weapon. You also get to fight alternate versions of Tiamat, Beelzebub, Asteroth and the Iron Giant named Yamata no Orochi, Beelzebub Soul, Lucifer and the Steel Giant, respectively.