The Mystery Of The Snail

How did this Brown Garden Snail ( Cornus aspersum ) manage to get where it is.  I found it on a hanging basket high up on a wall, suspended from a bracket which holds the basket away from the wall.  There was no obvious snail trail up the wall or along the ground near to the basket.  

I find  the way that their shells grow in spirals is fascinating, making beautiful patterns.