Maybe it's because I'm not an expert on castles, but I don't understand how that is considered one of the strongest fortresses on page 7? The outer walls aren't that tall and on one of them, it has a slanted roof that seem like it would make it difficult for defenders to stand on top of it and shoot arrows. Some of the walls are merely fences that seem like they would offer little protection against projectiles. And the hills doesn't look all that steep and unclimbable. The middle part of the fortress looks like it has a weak defense, which also means that the two ends of the fortress are easy to be isolated from each other as a result.