Our school built a new building in college. It was very shoddily built by a firm that didn't know how to build anything that big. So there was a lot of time for us to enter and explore the building before it officially opened since it was constantly getting permits and inspections. For example, one day during a heavy rain, water was pouring from around the plate of an electrical outlet. That caused some problems...
In the mean time, we found a way to get inside and figured out how to get onto the roof which gave us a view of the whole campus. At night, it was peaceful and beautiful. I watched the sun set from there one day. At the time, we were the highest viewpoint on campus.
One night, my buddy and I were headed for the roof. We had to go to the top floor then climb a ladder to an access panel on the roof. From there, we would crawl over a section of roof tiles that accessed the neighboring building (the only way to get there). Even if someone came after us, they very likely wouldn't pull the same stunt we did and, if they did, we could hear them coming and could scramble down the other side.
My buddy, insensitive to the most obvious of things, started to climb. But, as I ascended the ladder, I felt a fear I hadn't known. It almost seemed palpable. I could tell where it was coming from... At first, it was as if something was on the ladder looking down at us. I felt the fear move into the darkness away from the ladder. There was a small area between the top floor and the roof; it could almost be a secret room. The fear was emanating from a corner, as if something were as afraid of us as we, well I, were of it. I could never quite focus on anything hiding in the darkness, though.
That was the only night I felt fear. But after that night, I've had my fear of heights elevated. It was never as bad before that night.