I love these hunting missions in XIII

I just did the first type of mission where if you complete it then a barricade gets taken down and you can explore a new area. That fight was intense! It was great how when you approached it the whole air just turned blue, made me excited. Then I had to fight that Undying Cieth. What I like about these guys is that they all get some kind of introductory cutscene, like the other one I fought previously was flying around before you had to fight it. And it's cool because they're uniquely designed and look really cool. But yes the fight was intense, had to summon Bahumut around halfway and he turned the tide for me luckily. And then I explored that area it unlocked and, chocobos! Lots of them! I had to turn the TV down cause the collective screeching was so loud

But here's a question, how do I get on one? lol I assume there's maybe something you find later in the story progression like gyshall greens or something which I haven't got yet? I see that feather icon on the map, ran up to it, but it just kept running away from me.
Also, is Chapter 11 long? I'm at the point where you follow a flying fal'Cie to it's nest in order to find Vanille's village, but I don't wanna go there if it triggers off something and I can't do any more missions. But then alternatively, there could be more missions to get in that area it's in. It's hard to say, what I'm asking really is, is there any point in that Chapter that says something like 'If you have unfinished business on Pulse then take care of it before you go here'?