I found this large (about 3 inches) caterpillar moving quickly over moss and stones in a greenbelt area. It was difficult to get reasonable shots because it was moving so fast! It turns into a handsome moth in shades of white and brown (mostly brown), with a distinctive triangle shape.

The front end (the head) is at the right, the 'horn' indicates the rear end! though to my eyes it looks like the front.