There are some textures that are invisible but you can still stand on them.
If you have a "nodraw" texture on the wall, make sure you have the "Show nodraw faces" option enabled in the toolbar so that you can change the texture.
the map got fucked by bad saving (idk what happened i had saved it a bunch of times but it deleted itself also no you can see the texture but you cant see it from the other side of the wall and i WAS wondering what caused it but it doesnt matter anymore
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