For a closer look, you can go here and right click in the background > show background image:
http://www.davemckay.co.uk/iwd/iwd.php?area=ar1000

I also found this, it helps to understand the process:
The concept for Kuldahar:
http://www.davemckay.co.uk/iwd/image.../concept19.jpg
http://www.davemckay.co.uk/iwd/image.../concept20.jpg
The 3D mesh of Kuldahar
http://www.davemckay.co.uk/iwd/image.../concept31.jpg

So, I understand that the ground and the buildings are 3d. But what about the textures applied to it? Are they hand-painted (I mean litterally) or are they real photographs of differents grounds (grass, snow, earth...) ajusted in Photoshop?