My group is in the final stages of Book 5-- they've met and defeated the armies of the invader and are hitting the rebellion's leadership at home. IMC, however, "Irrovetti" is the leader of a rebel faction with fey support, and "Pitax city" is the capitol of "Brevoy", seized in a coup de main by flying in on wyverns.
One of my players, way back when we were generating characters-- about 3 years ago!-- had the idea that she had been a noble daughter and had spent time in the palace as a fosterling (read: hostage) to the Tsar. The character concept was "Sansa Stark with brains". She was also very curious and had explored the many reaches of the castle (like Arya), getting caught on at least one occasion overhearing conversations.
When re-organizing sections of the Kingmaker books, I thought of setting up the seizure of "Pitax", that the House of a Thousand Doors would be the Tsar's palace, and thus she would know the ins and outs of the place. She knew about the secret entrance (but not where it was in the river, that needed outside help), and most of the other secret doors inside. Thus, the group was able to infiltrate the castle from the bottom up and have the map of the upstairs revealed to them. I did not tell them about guard posts or NPCs or their locations, so that part's still being learned.
I was very pleased that I had found another way to pay back the player who had invested the most time and effort away from the table with me to work out her character's non-mechanical elements. I've done similar bits for other players, too, this one was just the longest in coming.
There's more for her, since the same player also created a missing half-elf mother who had been an adventurer. Thus, she's picked up that "Zuddiger's Picnic" is somehow tied to her mother's disappearance, and that's linked to the green lady and the magic sword that Mom was hunting for.
Has anyone else been able to do this kind of thing? For all of my gripes about this AP, being able to look far ahead and slip in links to individual characters has been one of the things I most enjoy about GMing it.
