Pippolazzo

Go back to the Underroot in Rhodochrine Jungle once you have the Crystal Key from Luna's gym, there's a puzzle involving crystals, rock smash and cut in the upper right corner with the Axew egg as final prize.

The north one if I recall right. It's definitely not in the Pyukumuku one, so you should look for the southern cave, which is accessed from a different area of the lake. It's smaller, you don't need blizzard to navigate it and it's basically a single room with 3/4 items lying around, including the readout.