Board Thread:Dragon City Questions & Answers/@comment-87.152.121.79-20130601100249/@comment-9946604-20130613010748

Frankly, if you haven't started this quest yet and you aren't prepared to spend money on gems, you may be too late.

There is tons of information on this already.

The Dungeon

The short answer:

There are 4 parts to the dungeon quest.

Beat the first quest for the dungeon island base (usless on its own)

Beat the second quest to get the dungeon habitat (an off-shore habitat)

Beat the third quest to get the Cerberus Dragon

Beat the fourth quest to get the Demon Dragon

And that's that.