Oh I see, thank you for clarifying :)

Clip of the glitch -

I was messing around with the letter clip in Metro Kingdom and I randomly thought it'd be funny if I climbed onto the taxi that takes you to the sub-area with the Sherms (and captured the video thumbnail). When I got down, I started going towards the city hall but when I got to the point in between the two crossings the screen transitioned and I ended up in the aforementioned sub-area. I tried it again a couple of times and it does seem to be consistent but I had brief look around various forums and couldn't see it documented (or even mentioned) anywhere so I thought I'd post a clip I took and explain it here.

I wasn't sure whether this was a known glitch or not or if it really has any use but just thought it was interesting that the entry method for the sub-area is not directly tied to the taxi itself.