These are some pictures from looking around inside the Bagley Mill, an ore mill near Silverton, CO that was built in the 1910's and abandoned in the 1920's.
Megalith by
Alex Burden, on Flickr
Ligneous Fossil Record by
Alex Burden, on Flickr
One side of the mill has collapsed (it suffered a lot of vandalism/stripping for wood), but the rest of it is actually pretty well-preserved for being over a century old and made of wood! Unlike so many other abandoned buildings, in this case the property owners put in extra supports and stabilized it in the 1990's. Three cheers for the owners and their conservation work!
Bagley No.3 by
Alex Burden, on Flickr
Timber Jungle by
Alex Burden, on Flickr
A lot of big funnels are scattered around and old machinery is suspended in the ceiling.
Rafters by
Alex Burden, on Flickr
Bagley No.5 by
Alex Burden, on Flickr
There's a lot of staircases that lead up for a long ways and then drop off into thin air.
Lightwell by
Alex Burden, on Flickr
A cool thing about buildings which are half-collapsed is the ambiguity of where exactly the interior ends and the exterior begins. How many walls does a room have to be missing, or how much of the roof must be gone, for a place go from being inside to outside?
Bagley No.7 by
Alex Burden, on Flickr