How do I get into the caves (for collectables etc. ). I unlocked the rocky cave but can't find it again now. Also are some of the caves only got to by skell? I am too low level (16ish) to get skells and have only just completed chapter 4. The follow ball will not work for places, just missions.
You can get into caves by going to them on the map. All except for maybe one or two are reachable without a Skell, although some of them are guarded by some high-level monsters (the one near the north-most point of Primordia, for example, is guarded by level 30s).
If it's not urgent to go to any cave in particular, it's easier to simply wait until you're a bit higher level before trekking throughout the land, looking for caves.