The usual method requires a precise count of steps, a ledge and a poisoned Pokémon. However, there is an alternative method that involves Super Glitch.
Requirements
Money to enter the Safari Zone. Access to Route 13. A Pokémon with Teleport. An available long-range Trainer and a free Trainer on another Route. Preferably a Pokémon with Fly. Preferably the Thunder Badge to Fly. A Pokémon with a specific move-set. Its first two moves must have 11 characters (technically 13 characters with 4Es included), and its third move must be Super Glitch. The fourth move is unimportant. Example : a Level 24 LM4 that knows Counter, Wrap and Super Glitch in this exact order.
Procedure
Prepare your Super Glitcher, a Pokémon with Fly and a Pokémon with Teleport. Fly away from a long-range Trainer to another location with a free Trainer. Battle that Trainer to get your start menu back. Fly to Fuschia City and enter the Safari Zone. Exit, say 'no', save and reset the game. Exit the Safari Zone and say 'no' to activate the Glitch City glitch. Go to Route 13 (east of Fuschia City) and keep walking around until the 500 steps run out. You'll be warped back to the Safari Zone gate, exit to enter the Route 13 Glitch City. Press the start menu and open the Pokémon menu (important), then switch your Super Glitch Pokémon to the first position and Teleport away (important you use this instead of Fly as Flying will update the screen data). Walk back to where you flew away from the Trainer-Fly glitch Trainer and the menu should pop up. Press 'Save' and the F9h box-set will appear. Press 'No'. Exit the menu. A battle will begin, with the Gym Leader theme playing. The game will also state that the Pokémon is hooked. End the battle, the overworld palette will be glitched. Jump off a ledge and you'll stay in mid-air and will be able to walk through walls.
Video Demonstration
REDIRECT Template:YouTube
See also
Walk through walls trick (ledge method)Walk through walls trick (museum guy method)
Walk through walls trick (select glitch method)