Knot Island
After defeating the Fire-type gym leader Blaine on Cinnabar Island, a character named Bill appears to invite players to the Sevii Islands. After accepting the quest, players are taken to the first of these islands, Knot Island, which is home to Mount Ember. To get to the mountain, head northeast from the Pokemon Center, past several trainers and regions of tall grass. Pass through the Ember Spa and then head north into the mountain.
Team Rocket
Long-time Pokemon bad guys Team Rocket are back. While players first encounter them towards the start of the game, and even infiltrate their headquarters, you will encounter them again on Knot Island. If you've beaten the Pokemon League, enter Mount Ember and head to the left where you'll find two Team Rocket grunts talking. One will mention part of the password to their Warehouse, saying "Goldeen need log."
Battling the Grunts
Both Team Rocket grunts are fielding Pokemon around level 35. You'll need to battle both of them to proceed through the secret entrance they're guarding. Use a Water-type Pokemon to easily defeat them, since both have a few Ground-type Pokemon with them. This battle should be easy since you've already defeated the Pokemon League.
Exploring the Cave
After you've headed through the secret entrance, you'll find yourself in another cave on Mount Ember. Use the move "Strength" to push the rocks around and head south. You'll find a large chamber with stones that translate braille, and if you head south, another room has braille lettering that reads, "Everything has meaning. Existence has meaning. Being alive has meaning. Have dreams. Use power." Head down the steps to find a ruby lying on the ground. After this, you'll want to backtrack and head back the way you came to leave the cave.