Captain Grot's Treasure, Foul Dale, Crooked Oupost
The key to this quest is in the water of the Ancient Crater. North of the crooked outpost and south of the crater. It is on a shelf with a pink mushroom on it. There is a round wheel to manipulate there. This appears underneath the "'N"" on the mini-map. Captain Grot's Treasure box is behind the middle tree at the back of the Crooked Outpost. The area has a fence around it, with a short fence you can easily jump over in between the two taller sections of fence. Over to the left is a path to go to the Ancient Crater.
This post has been edited 2 times, last edit by "u_176173515" (Apr 14th 2020, 7:46pm) with the following reason: additional information