Virtually a Ladder

I was trapped on top of a tall building or tower, been there for ages.
I looked over the wall and saw a steel ladder, fixed vertically to the wall, descending to ground level about 60 feet below.
Why had I not seen it before? Possibly because it seemed to blend with the stonework. Was it really there?
I swung myself over the wall, grasped the top rung and started to descend. The rungs were hard to hold onto as they were so close to the wall.
Suddenly my heart lurched, the ladder was no longer there, just stone work. I was gripping onto stone edges. Please come back. Then the ladder gradually reformed, but hazily. I descended even faster before it or I decided it wasn't there again.
Perhaps the world is what you make it.