These lovely snails are on the wall of a ventilation shaft for the railway.
Until a week or so ago there were shrubs covering this part of the wall and the snails must have taken up residence there in the nice cosy shade of the vegetation.
Now the council have dug out all the shrubs and laid the snails open to the cold and to predators. There are plenty dead ones on the ground below.
Keeping an eye on them on my way to work.