Ploymus Mountain Cave is east of Zora's Domain, southeast of Mikau Lake.
Cave Location
Ploymus Mountain Cave is located at 3660, 0539, 0272, which is east of Zora's Domain. If you have completed the quest Restoring the Zora Armor, you can go east on the bridge from Zora's Domain to reach Mikau Lake, use the Zora Armor to swim up the waterfall, then go east to find this cave.
Cave Features
Near the cave entrance, on the right side (i.e. the south side), there is a ledge with a luminous stone deposit. You can place a tree trunk on top of this ledge and use Ascend to get on top of the tree trunk, and you will find a tunnel. At the end of the tunnel, you will find this cave's Bubbulfrog.
There is a constant rainfall in the cave, making the walls slippery. You can go outside and cut down a tree and use it to climb up the platforms, or use the tree as a ramp, or use the tree to help you use Ascend to go farther up. Or if you have Sticky Elixir or the Froggy Armor, you can just climb up.
Reach the ledge at the southeast end of the cave using one of the above methods, then go to the end of the tunnel to find one of Misko's treasures: the Climber's Bandanna.