Going Ape

The plan today is to "Go Ape" (http://www.goape.co.uk/) out in Haldon with some friends. I understand this involves swinging from tree to tree and whizzing down zip wires. In my mind this was a fun thing to do on a rare Saturday off, but this morning I was imagining being up high in the trees looking down at the floor and I felt a sudden moment of panic, and remembered that I am quite scared of heights. If just thinking about heights has that effect then what will the actually experience do? In just a few hours I will find out.