That water dragon wants you to meet the earth dragon, who is located on the plains below Isthmus' Castle's southern exit. If you don't see it there you should be able to learn the location of both it and the shortcut into the empire from someone in the town on that map.
To open up map locations you might have missed:
Crystal City should have someone that reveals the Steppes, which has two northern exits. The left one leads to a desert, which is added to the map after you exit it from the east, and the right should lead you to a map with an oasis town in it. People in there can tell you about Northpoint, which has boats running to an island with a pyramid.
The island with the pyramid has three locations on it and you can learn about all three from whichever port you land in (as I recall).
Recruiting Claudia and Grey should have unlocked the empire for you, which you use the shortcut or cross the plains from Bruelle to reach.
The empire has a port with boats that run to the pyramid island and the volcanic island where the Bird wants you to go -- I forget which boat is which though. You can talk to the people in the town to learn about the volcano and the dinosaur plains there, though. That should be all of the major map locations.