Final push - Canal key?

[Anderic]

so i'm in the final act i'm heading through Paradis towards Ludwyn, and an NPC i helped earlier gave me a key to help avoid some combat. yet there's no clear door that this key goes to.

[Anderic]

ok i found door to the canal, but only because i came at it from behind. the "door" is hardly distinguishable from a make-shift wall. I would never have found this from the side i was supposed to use the key on.