Of course, terrain doesn't play such great gameplay role in fantasy war game like in their sci-fi counterparts, where you need to seek cover between the ruins or in abandoned factories. However, you can't create a proper atmosphere without a nice terrain. Let's have a look at some bright examples found on the Internet. If you know the authors - please, tell us in the comments - you'll help a lot.
You can create a nice fantasy terrain even from industrial buildings for Warhammer40K
Baleful Realmgates для Age of Sigmar - is a great example of how beautiful terrain from the official manufacturer can be. Besides, it has it's own special rules.
Such building will do great for skirmish, like Malifaux.
Another example of great terrain for Age of Sigmar from Games Workshop.
Chaos Dreadhold - is one of the most expensive sets of terrain ever. The full kit with all the towers and gates will cost you more than 100 pounds.
The best match for such fortress is something like gaming mat Hagland
Realmgates again. They are great if you want to train your flame-painting skills.
This terrain looks self-made, but it's really great.