Grimrock

I'm not stuck or anything, just a question I can't answer for myself. I found a note lying on the ground in Level 4 (Beast Garden & Menagerie, accessable through the north-west teleporter) which i will provide a picture of at the end of my post. I found a similar note a few levels deeper on an earlier playthrough, so I'm pretty sure that this note shows corridors/rooms which are actually on the map. I hadn't any trouble finding the spot for the note i found later, but I cant seem to find this one.
Help would be appreciated, if it doesn't spoil anything.

That is a map to the slime dungeon. You can get there from level 3. Compare that map to level 3 map and see if you can find the entrance.

Aww I hoped it was something I haven't found already, the big weird looking thing in the top-right should have given me the hint. Thanks alot anyway!