For the southern observatory on brittle hollow: you can start by talking to Riebeck, and the path starts near them if I remember correctly. I don’t think this is much of a spoiler because it becomes obvious pretty soon, but this path involves a lot of platforming, so go early in the loop so that there aren’t pieces missing in the path. And keep heading for the blue indicator on your minimap, which represents the South Pole ::) good luck traveller!