How do you get to it?

had a great day today and got some good photos.
I think this is quite simple but the colour change gives it something extra in my opinion..

I have no idea how you get on/in to this place or what it is, From the sides of the banks you can see no way up to it even if you could walk on water and get to it!!!!

Anyway... 3pts to anybody who can tell me where this is?

A clue.... Its in a Well known district for people who like walks...