Walkthrough: Just off Big Wave Beach is Sandy Cave. This cave is on the smaller side, having several different areas divided by waters. Outside of having a few items and Wild Pokemon, there isn't much to it.
Wild Pokemon:
Initial Pokemon (Levels 6-9): Zubat(70%), Psyduck(30%)
Trainers:
There are no Trainers found in Sandy Cave.
Items:
Big Pearl - On First Island
Light Clay - Southeastern Cave (Requires Sharpedo Pager)
TM24 - Northern Cave (Requires Larpas/Sharpedo & Machamp Pagers)