The Beryl Cave is accessed west of the Beryl Gym with Rock Smash. It leads to the Rhodochrine Jungle Totem Area, and after obtaining Rock Climb, you can also access a part of Teknite Ridge.
1F, Rock rubble on the right side of the cave (Hidden)
Blue Shard x2
1F, Space 4 spots right and 1 spot down the rock in the top middle of the cave between the 2 ledges (Hidden)
BF2, Rock on the right bellow the up-ladder (Hidden)
Ether x2
1F, Big rock bottom right side at the left side of the cave (Hidden)
1F, Space bellow the rock top the down-ladder at the left side of the cave (Hidden)
When you go through the cave, you’ll see a Nidorina trapped in one of the cages. Open the cage using the switch found in the other cage. Show it the Silver Ring from the Beryl Gym and it will go with you. If you check the summary of Nidorina, it says the original trainer was Corey. Nidorina has two Egg Moves in its moveset: Venom Drench and Disable.