You need to find 3 of these, 1 is at the waterfall on top of Luna's gym puzzle, another is in Azurine island I believe and yet another is locked to the end of the trade quest that involves the horrible dive locations and knowing which npc you need to talk to in order.
The reward at the end is one of Lin's puppies.
>>56067853I think it's said she found this place during a hike, it's never explained exactly what it is, but it's not the only place in the desert where really is really screwy.
Also did you find the mirage tower? It's miserable to reach it since you need to find the 3 mirage oases.
