The hospital that Charlotte was in. Allison visited her here. 

This is the bridge that patient Number 27 attempted suicide. It's located near Regent's Park where she would wait for Dr. Dunlop Strange, and in chapter XXI we see Mary as she, "[pauses] on the North Gate Bridge, she looked down into the dark canal water, on to which the last shivering autumnal leaves were slowly fluttering down. She thought of the girl- of Number Twenty-seven- who had tried to drown herself in those greenish, slimy waters" (21).  

Camera Obscura