Pokémon Ruby and Sapphire/Granite Cave

A Letter for Steven
When you arrive in the Granite Cave, a hiker will give you HM05(Flash). This will help you see in the dark cave and reduces the opposing Pokemon's accuracy in battle, though you'll need to get the Knuckle Badge from Dewford's Gym Leader Brawly in order to use it outside of battle.

Head west and grab the Escape Rope. Then go down the nearby ladder. On the next level, search the passage south of the Mach Bike slope for a Poké Ball. In the bottom right corner, go down another ladder.

On the third level, head west to find some stairs. Walk up, then move right to find a ladder. Be sure to check the white rock on top of a platform near some rocks you can Rock Smash to get an Everstone. Go up, then move a couple squares left and go up another. Back on the main level, run to the west to find a cave entrance. Head inside and talk to Steven. Give him the letter, and he'll give you TM47(Steel Wing), a Flying Type move that deals damage while possibly increasing your Defense. If you have a pokémon with the HM rock smash, smash some rocks and a should turn up.

Daring Dash over Crumbling Floors
Once you get a Mach Bike, you should return to the second floor of Granite Cave. Go to the slope that you couldn't walk up. Your Mach Bike will easily be fast enough to ride up the slope, granting you access to a new area of Granite Cave.

Once you're up, go down the ladder for a Repel. Climb back up and ride your bike across the cracked floors until you touch the wall. Don't stop halfway or you will fall to the floor below and will have to climb back up. Go all the way up the wall and go past the second set of cracked floors until you reach the second ladder. This ladder acts as a checkpoint, so if you fall through the floor you can try again from this ladder. The final set of crumbling floors are a little tricky. You must go right, down and right without hitting anything, or you'll lose your momentum and fall back down. Once you've past this stretch of floor, go down the final ladder for a Rare Candy as well as an Everstone hidden inside the white rock.

Items found

 * HM05: Given by the Hiker at the entrance.
 * : Near the ladder on the top floor.
 * : One in the darkened area near the smashable rocks, hidden inside the brightly coloured rock. The other one is located right next to where you found the Rare Candy hidden inside a similar rock.
 * : The passage south of the Mach Bike slope.
 * TM47: Given to you by Steven after delivering the letter.
 * : Requires Mach Bike. In the darkened area, use the bike to climb the slippery sand, and fall into the cracked floor.
 * : Requires Mach Bike. In the darkened area, use the bike to climb the slippery sand. Use the bike to speed over the cracked floor.