Head around the magnetic boulder to Anna’s right and up to the ledge North of it- a yellow shard is waiting in the glow of the high-floating rock.  Head off to the East into a side-nook to pick up a Hyper Potion that you really don’t need just yet- restoring 200 HP instead of 80 (via Lemonade) isn’t much of an improvement when none of your team members are likely to have more than 100 health to begin with.

Just South of the dead-end you’ll find two magnetic shards blocking your way- shove the Northmost one to the West, and then push the other one South and you can squeak through on the narrow ledge.  Descend the stairs and head right, then climb some more stairs to the North of the electrified boulder.  Check the outcrop to the right and you’ll find another Hyper Potion, but that’s all there is to do here.

Turn South and you can head out onto a long jut of rock leading to a bridge.  Cross going East and you’ll be stopped partway when you hear a voice enthusing about the cave.  Whoever it is rambles about the mathematics of electricity and how the energy relates to people and pokemon, then talks about having to do something to save pokemon and protect someone by stopping them.  Whoever it is then leaves before you can spot them.

Continue to the far side of the bridge, where you can shove a floating rock out of the way to the South, then head South yourself.  Waiting by a stairway down is a trainer itching for battle.

Battle: Ace Trainer Corky (1997 Poke)
Opponent: Klink Lv 33, Unfezant Lv 33, Klink Lv 33

Be careful- this is a 3v3 battle, and pokemon on the left won’t be able to attack or affect pokemon on the right- which means that if the order your team is in doesn’t match well with the order of Corky’s pokemon you can easily wind up taking a turn or two of damage while you rearrange your battlers one at a time.