I found this weird glitch

[The name master]

While using some walk through wall codes, I happen to come across this glitch in all version of gen 1

I haven't seen anything about this on the internet anywhere (yet) and I don't think it's the codes either.

Walking through the entry building to the indigo plateau will completely glitch the Kanto region, making it look like a glitch city glitch. Graphics are screwed, but nothing else. Entering a door or entering a battle or flying will reset the graphics. If you want to explore the whole Kanto region (or at least most of it) you have to go the long way round, through Cinnabar, but there's a high reset chance through encounters. Going the normal way, you have to pass a door to Viridian Forest, resetting everything.

Interestingly, through the front of the Indigo Plateau will glitch some of the graphics there and will disappear when you talk to an NPC, but will reappear when the text box is gone.

I may be the first person to discover a new glitch! Not really sure if that's something to be proud of

[Captain Jigglypuff]

You've found Glitch City. It's one of the harder glitches to find but people have known about it for years. I've seen the info about it on another site and in YouTube videos. I don't think people talk about it because it has to be triggered by very specific events.

[The name master]

You've found Glitch City. It's one of the harder glitches to find but people have known about it for years.

There are many glitch cities but I've not seen or heard of this one before (not even on the internet) so I' wondering, have I found a glitch city no one knows about?

If I have, I'm surprised people know how to encounter missingno, but never thought to do this.

Also, could anyone explain this particular glitch city, as in how it happens?

[To4oo4]

There are many glitch cities but I've not seen or heard of this one before (not even on the internet) so I' wondering, have I found a glitch city no one knows about?

If I have, I'm surprised people know how to encounter missingno, but never thought to do this.

Also, could anyone explain this particular glitch city, as in how it happens?

Here's a Bulbapedia article on it, if that helps.
https://bulbapedia.bulbagarden.net/wiki/Glitch_City

[The name master]

Here's a Bulbapedia article on it, if that helps.
https://bulbapedia.bulbagarden.net/wiki/Glitch_City

There doesn't seem to be anything about the particular glitch city I found.

Actually realised you can get through Viridian Forest by walking up through the trees to Pewter City.

[To4oo4]

I'm intrigued now. Was this in Red, Green, or Blue?

[Petzbreeder]

you don't think it was the codes, but could you tell me them anyway?

It is against the rules to share cheat codes here.

[The name master]

I'm intrigued now. Was this in Red, Green, or Blue?

Pretty sure it works in all versions of gen 1 (Red, Blue Yellow and presumably in Green, idk tbh) if you want the codes, I can give to you through PM, as codes are not allowed on the forums.

EDIT: I have a theory. Maybe it's the Gameboy's limited memory and the Indigo Plateau's (I think) unique tileset, the Gameboy is probably using a lot of it's memory to load these tiles, but when it tries to load the other tiles in the other areas as well, it's memory is too full/busy, so ends up placing glitched tiles instead.

Also, you have to go AROUND the building from the back, not through it, otherwise the game will crash.

[Shade_]

This is a variation, albeit less common, of a well-known glitch called 'Glitch City' which is when the overworld's tile set(s) are scrambled into a nonsensical and often times un-navigatable hodgepodge.

Basic information: https://glitchcity.info/wiki/Glitch_City

The most well-known is the 'wrong warp' variation in which you invert the Safari Zone so that you're entered into a session when you leave.
What you've triggered is the 'stepping out of bounds' variation:

An out of bounds Glitch City in Pokémon Red, Blue, Yellow is a type of Glitch City that appears when the y coordinate of a map is a certain value higher than its y boundary. It is not to be confused with a Generation II out of bounds Glitch City.

It can be contrasted with a Phantom City; which is a copy of a map that appears for excessively high x positions greater than the x boundary.

The required y coordinate for an out of bounds Glitch City may vary[clarification needed].

Like Glitch Cities accessed from a wrong warp, they are typically sourced from an existing map but with an invalid map block source pointer.

Accessing an out of bounds Glitch City
Use a free travel walk through walls glitch.
Go to either the north-west most or north-east most corner of a map (where y=00), then walk west or east. Alternatively, the glitch may work when y ranges between 01-06, with 06 placing you at position FE, 05 placing you at position FD, etc. The map you set up the glitch from must have a real east or west connection.
The y coordinate will be corrupted. Keep walking up to see a Glitch City.

https://glitchcity.info/wiki/Valid_source_map_Glitch_City#Through_stepping_out_of_bounds