The Heart of the Lake

"Hey, you want to hear a rumor? I hear there's a cave beneath the lake that contains a mystical meteorite. Here's how you can find it."

[*] Get a Pokémon that can use/has Dive.
[*] Beat Kuaisu, the gym leader of Lividus Town, to gain his friendship and trust. Ask to borrow his scuba equipment.
[*] Dive with your Pokémon to the lakebed.
[*] Roll between 15-20 (out of a d20) to find the cave entrance, or perhaps come to terms that it does not exist.