Before:

After:

Download smaller Photoshop file:
http://www.bloomi.de/images/markgrafenbrunnen.psd" onclick="window.open(this.href);return false;
The grey layer you see is just for extra graininess, I ran the highpass filter with 2 pix over it and blended it.
Here is one 100 % crop from the center, notice the spider web

