I found that one of the bridges int he lower parts of the administrative district doesn't quite go all the way into the wall so you can slip inside. Thankfully the trains just go through me.

https://i.imgur.com/zLCt22y.jpg (Where the gap is)
https://i.imgur.com/waEaYIs.jpg (Inside, this is far as I can go, collision is only one-way so I fall through if I go further)