I visited Conwy (north Wales) on holiday back in 2005. Before going I modelled the castle as if it were under siege. The real castle would have had whitewashed walls and so appeared quite different - here the wall material uses a photograph of the walls I took myself. I never quite finished this as intended; I wanted to have some more views with extra siege engines and a larger assaulting army. Back then my system specs didn't really make this feasible. Many of my earlier projects stalled not so much from lack of motivation as from the sheer inconvenience of rendering multiple passes very very slowly.
Terragen was used to create the terrain, which is only a very rough approximation of reality. I should have compromised the realism a lot more on this. The siege weapons are placed absurdly close to the walls and the attackers have nothing to protect themselves. The ballista at the foot of the stairs is quite nice though.
The castle itself was modelled on plans I found online, so it's pretty accurate. When actually walking the site, the one major difference I found was that the interior of the caslte feels much larger than is shown here (even allowing for the fact that many interior buildings are now missing).