Glitch city can be found in Red, Blue and Yellow.
To get there go into the Safari Zone and go up to the house then back down out of the Safari Zone and say No to the question. Then go back out again and say No. Then save your game and turn it off. Then turn it back on and go out of the Safari Zone. This time the man won't ask you the question. Keeping going down until he asks you if you want to go in. Say No and go out the door. Next go to Cinnibar City and keep surfing on the coast for a little while then you'll hear Pa say Ding Dong. Then you will be tranported to the Safari Zone. Then go out and you'll be in Glitch City… You can catch high level Tentacools and Tentacruel here, and you can surf of the ground. But be careful, you can get trapped in here, well FOREVER… to get out just Fly out with one of your Pokemon