I might as well add to this thread with some photos from our second trip, where we got to see some less known parts of this well known place.
This time, we made it down under the mill to see the remains of the turbines and some very neat stonework. 28: Tailrace
Two levels below the partially-collapsed flooring are the tailraces that carried outflow water from the turbines to the river. 29: Curly Pipe
Pipes were made like this in the late 1800s. Most of this part of the mill was built between 1860 and 1890, and continually rebuilt in many ways through the early 20th. 30: Outflow Pit
To the right, one of the big outflow pipes plunges down into the mud. The mud here is probably a few feet deep and way too soft to stand on. 31: Arch
There are five of these tailrace tunnels, all linked together and made of really diverse and pretty stonework. 32: Line Shaft
There were four of these big turbines, maybe five, maybe more. This big line shaft passed through them all, with a few clutches and flywheels along its length. 33: Flywheel
These flywheels on the line shaft probably once had flat belts running up to the machines above. In the mill's later years they might have run generators instead, but it's obvious that these turbines were slowly abandoned one by one over the years the mill was active. 34: Close/Open
20th century tech mixes with 19th in the line-shaft tunnel. 35: Basement
In a different section of the mill, this basement shows a lot of rebuilding and repairing over the years. 36: Nutmeg Club
This brand of soda from New London CT doesn't exist anymore. 37: Outfall
The other end of the tailrace in 28, on the river bank. 38: Other Outfall
the brickwork here looks identical to a drawing from 1866, so it's probably original. 39: Atmosphere
it started raining as we were on our way out.