Things You'll Need
Instructions
Enter the cave then use the "Flash" ability to light up your surroundings. Without Flash you will not be able to see where to navigate through the caves.
Walk right until the tunnel branches upward. Stick to the upper section of the path as you will be jumping down ledges and won't be able to go back. When you reach the wall on the right, go up and then descend the ladder you find at the end of the cave.
Walk down once you get to the bottom of the ladder then left as soon as the tunnel branches. Continue left until then go down the first opportunity you have. Go down the ladder you see.
Walk down and speak to the bald man that is blocking your path. After the conversation you will lose your "Silver Wing" inventory item but he will give you access to the path behind him. The "Silver Wing" is the item you received from clearing out the radio tower earlier in the game.
Follow the path behind the man. The first entryway you reach leads to a "rare candy" so enter and pick it up if you want. Continue down the pathway and take the entrance right at the bottom.
Approach the five girls wearing kimonos to trigger a cut-scene of them dancing. You need the item called the "Tidal Bell" in your inventory to trigger this event. This item is found by defeating the five girls in Ecruteak City earlier in the game.
Battle Lugia to lower its health then capture it to complete your journey through the caves. After you have Lugia, you can either backtrack to reach the exit again or use the "Fly" ability to go directly to another city. You can explore the rest of the tunnels in the caves but it doesn't lead anywhere story related.