A History of the Fortress
Having looked at the history of the inhabitants of the Fortress, we should look at the history of the physical structure itself. Obviously there isn't a lot that can be said on this topic, but looking closely we can find various hints as to events which have transpired within its walls.
Who exactly built the Fortress and why, we cannot tell. One thing we can tell is that its construction was interrupted; the water tower and the area around it are mostly scaffolding. This is the only area of the Fortress which appears to be incomplete, so it is likely that this was a later addition or some final work being done, rather than being initial construction which never got completed. This scaffolding is in remarkably good condition considering how old the Fortress appears to be. We know that the Queen's power is holding the Fortress together. In fact, the Queen's power is probably keeping it in exactly the state it was in when she started exerting that power, except in those areas where her power has weakened. This is why we see wooden scaffolding which has withstood the test of time, while there are other areas where walkways and entire rooms made of stone have long since fallen into ruin. Any part of the Fortress which she protects remains as it was when she started protecting it.
Assuming that the Fortress was in good condition when the Queen took over in her dark form, it seems that it has taken damage over time. We know that the Queen is close to death during the events of Ico, and it is likely that the areas of the Fortress which are seen to be damaged reflect her losing her grip on both the Fortress and life, just as the collapsing of the Fortress reflects her death. What is interesting is that many of these areas have been made easier to navigate by the addition of chains which allow access to otherwise unreachable areas. There are also other small signs of reparative work such as boarded up windows.
Written by Crumplecorn