Underwater door in the sewers

[Henk]

On the main sewers map there is a wooden door underwater in the reservoir area, in the bottom right corner of the map. How do I open this door? I've explored the entire map but haven't found anything, so I guess it's a secret button?

[The Doppelgamer]

I would really like to know about this too, I search that entire room (in the water and everything) and I couldn't figure it out. Is it just there for looks?

[Depili]

There is a hidden button

SpoilerShow

in that room with the said door, underwater, in one of the 1-square columns.

[The Doppelgamer]

There is a hidden button

SpoilerShow

in that room with the said door, underwater, in one of the 1-square columns.

Damn it how did I miss that?

[Henk]

There is a hidden button

SpoilerShow

in that room with the said door, underwater, in one of the 1-square columns.

Thank you

[AsgarZigel]

How do you get to the green gem behind a grate in the same room?

Edit: Nevermind, found it.

SpoilerShow

There is a secret button in the "follow the leader" puzzle, on the middle pillar connected by 2 bridges.