This beautiful, mechanically mysterious old lock belongs to a door in Sweden.
If you have a genuine old house, this is probably what the insides of your rim locks look like!
Aside from being a fascinating subject, it is a great photo – love how the hints of green patination on the round face in the middle of the photo echo the green grass, and the textures in the photo just seem to leap out at you.
Looks like the key would have gone in the other side of that bottom left thiny with the coiled metal around it. Would have taken quite a lot of force to open your door! On the upside, can be opened from the inside with just a flat headed screwdriver.
I disagree. The key would have been inserted opposite the hole in the large round plate. On most of these old locks, the keyhole would be aligned horizontally. Turning the key raises the large tapered section which is attached to the latch. The latch is the bar which is pressed down by the top spring (coiled metal at the top). Behind the tapered section will be a notch on the bolt (the bit which sticks out to the right and actually locks the door). Further turning of the key will engage the notch on the bolt pulling it leftwards, since it’s now free of the latch, and opening the door. The coiled spring on the left recloses the bolt when the key is released.
Sounds like you know about old locks, Carl, thanks for your comment!