TuffStuffMcGruff,

Kerak de Chevaliers is located in a arid area, on the outcrop of a hill. This hill has very steep slopes on three sides, so the castle is only accessible on the side of the three great towers of the inner ward... I do not have a link to the picture at the moment... IRC, looking from above, the spur looked U shaped, with the only accessible side being on top of the U, and directly facing the great towers...

Talking about inaccessible castles, there are quite a few in the Pyrenees, and in Germany. The most awesome location I have seen for a castle though is in Italy