Zanarkand Ruins
Travel to the Zanarkand Ruins and a cutscene will play as soon as you attempt to make your way towards Zanarkand proper. Continue towards the ruins, through the dome, and into the hallway where you will meet up with Isaaru. Have a quick discussion with Isaaru to kick off an optional side quest that you can complete right now.
Operation: Monkey!
This optional side quest can be completed in either Chapter 2 or Chapter 3, but you might as well do it while you’re here. Of course, this side quest is not optional at all if you’re aiming for 100% Story Completion.
Side Quests
Matching up each of the monkeys that are loitering around the Zanarkand Ruins with their partners.
Completing “Operation: Monkey!” doesn’t add any Story Completion Percent on its own, but it does unlock a scene in Chapter 5 that only plays if you’ve matched up all of the monkeys. If you do it now, make sure you check it off as done, but you can also do it in the next chapter.
There are also all sorts of treasure chests that you can open, identified on the maps below, but you can grab these as you’re completing the optional monkey quest.
That’s everything here. With all three 
Syndicate Uniforms in hand and every other location visited, it’s time to head to Guadosalam to progress the story.
Checking the “Zanarkand Ruins Complete” box adds the Story Completion Percent for the automatic scenes in Zanarkand Ruins.