Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
An observation tower located on a hillside near Kaer Morhen caught Geralt's eye. Though the structure had been there for as long as he could remember, this was the first time in ages he had bothered to inspect it more closely. When he did, he discovered a whole heap of wraiths had taken up residence within. I've said it before and I'll say it again - witchers make horrible housekeepers.
