Taken from http://db.gamefaqs.com/console/snes/file/final_fantasy_iii_j.txt
-- Acquiring the Water Rondo dance --
Place Mog in your party. Head over to Nikeah and grab a chocobo. Ride it all the way to Barren Falls and take the plunge into the water. You will end up on the Veldt. Head to Cresent Mountain and jump into the water.
This time, head left at the first juncture and left again at the second juncture. It is faster than the way you originally went with Sabin, but since you do not need to get the treasures this time, it is faster.
You will wake up in Nikeah. Exit the town and your airship is waiting for you.
There is no way I would've been able to beat this game to my satisfaction without FAQs.
^_^