POKEMON RUBY AND SAPPHIRE TEAM AQUA'S LILYCOVE HIDEOUT

From the first room, you'll go through the door and end up at A.

After entering through A, head through 1 to get a Max Elixir. Pass back through 1 and go through 2. You'll want to go through 3, so head there and work your way through the puzzle:

You'll end up in a room with four item balls, two are actually Electrodes, but there is also a Nugget, and an extremely valuable Master Ball. You must get this now or you will not have the chance later. Make your way back and head through 8 and then up into B.

Head through 9 to grab a Nest Ball. Follow the pads numerically and you'll see yourself near the stolen submarine. Pad 12 will take you back to the entrance.