Found an interesting one by accident, you can softlock yourself in Location A of the Mill on the Third Locus by doing the following:
- Move Lyra somewhere towards the middle of the bridge in Location A
- Save the game
- Quit to title (closing the game accomplishes the same thing)
- Load your save
- Use the Eidoscope twice
After that you should be on the lower floor with no way to get back up.