At the Altis Hospital in the biggest city, you can't climb a ladder. So if you try to climb it down from the top, you will get "Climb it up" or something, but if you select it, you can only climb it up and stop there where it started. If you climb down, you will fall down and break everything. On the bottom of the ladder it is the same, just the opposite. Instead of Up you get "Climb down". So the ladder is actually nonuseable.