Parch

Go to the Apogee islands... They are at the far east of the map, the furthest away from the mainlands (hence the name apogee) And there is a big raindrop statue in the middle of the town, use douse on this, and it will show a cut-scene of a trail going to a blue rock on an island just south of apogee... (like Air's rock south of Alhafra, and Mount Mikage on Izumo, and Magma rock north of Gabombo, later in the game) well the challenge here is similar to the one on Air's rock (which you should have passed by now) and when you complete it, you will get parch. I have to say that this challenge for me was the hardest of all the four 'rock' challenges.