Osamělá věž is where we find what is initially described by a messenger as a striga on the loose in Stará Wyzima. A bit more investigation reveals that while there may well be a striga on the loose somewhere, the thing on top of the tower is definitely not a striga, it's a mutant "like [Geralt]", as Kalkstein points out. This little scene also serves to alert the witcher to the alchemist's presence in the old quarter.