When you come to the section where the stairs of the fire station's tower are located, climb up to the third floor of it (1. one has a blue closet, the 2. has a shelf and the third one nothing) and face towards the side of the wall where the ladders are outside of the tower and you should be able to see and click the "climb up or down the ladder" -button. I'll post pics of this bugmas soon as possible!