(https://s19.postimg.cc/5k45hv0qr/mystery_3.jpg) (https://postimages.org/)
Come on folks. This can't be that hard, can it? Someone give it try and you might get warm.
Well [L] I thought everyone knew what it was. They work in [L] too.
It is a fire extinguisher. Once removed from the wall, there is a release valve on the bottom which will cause water to shoot up like a fire hose once it has been popped.