Travel to any of the Aerodromes and search for the attendant labelled “Private Airships”. Speak to her and choose to board the Strahl. Select “The Ridorana Cataract” as your destination.
There is a short cutscene that takes place as your team arrives at the Ridorana Cataract for the first time. Make sure that you set up a 
Libra Gambit for your travels through this location as it is loaded with traps.
That said, this is a fairly small zone that is a precursor to the much larger dungeon coming up: the Pharos. You can use the anchor in the ground near the edge of the cliff to return to the Strahl at any time. Travel east and use the Save Crystal.
The fastest way to reach the Pharos and continue the game is to head north. To fully complete the area though, head southeast into the next zone to enter the Colosseum.
From the center of the Colosseum, head north and take the first pathway on the left. At the end of this path you will find the green Urn with the map of the Ridorana Cataract. Continue north to leave the Colosseum into the next area.
Be careful as there are a ton of traps close to the blue Save Crystal at the top of the steps. Save your game and proceed into the next dungeon by heading east.
Use the map below to help you navigate:
(Click on the map to enlarge)
