Pokémon Ruby and Sapphire/Sky Pillar

How to Find Sky Pillar
Sky Pillar is on Route 131, to get there you need to beat the Elite 4 and have a Mach bike. To get there from Sootopolis head East, pass the Sis and Bro and the Female swimmer, then go North between the Male and second Female Swimmer, there should be a gap in the rocks, go West and follow the path and you have reached Sky Pillar.

Follow the cave through and you will come out viewing a tower, you can get Pokemon from around level 48 to around level 68 in the tower (the level inceraces at you climb) at the top there is the legendary Pokémon Rayquaza at Level 70, It is a dragon and flying type and is powerful. To get to the top you need to use your Mach Bike to navigate the cracks to reach the top.

Strategies to catch Rayquaza
As with any legendary, save before you battle so you can switch the power on and off to get another go.

Stock up on balls, you probably need about 40 ultra balls (to be safe) and 15 Pokéballs (I'll explain later)

Get a Pokémon that can put Rayquaza to sleep, use the ultra balls then because you have more chance to catch it.

The Pokéballs are used for when Rayquaza uses Fly, use them because it doesn't waste a move and there is less chance of catching it when it is flying. Catching Rayquaza with a Pokéball is also one of the best things to brag about (it is possible)