Terrain building is more fun with a constant stream of inspiring sources. Look outside the typical hobby forums for photographs (and photoshops) of real life.
Source: bpkelesy photo used without permission
Could this become a Hirst Castle on an ice peak? Why does our gaming terrain always have to be flat!
It does not take Photoshop to make something incredible, history is still in the world around us. Travel logs are rich in photos of castles, forts, churches and abbeys.
The world of architecture has plenty to offer:
Deviant Art is a constant source of images, both real and imagined. Search by Urban and Ruin for a world fit for any battle field.
Painting decay, rust and ruin can be difficult to master. Look to real examples to get the tone right at Smashing Magazine.
Source: daniel cheong photo used without permission
Finally, web design sites provide a plethora of textures. Look at steel, stone, marble, rust and bone for real world color.
Chicago Terrain Factory 