These are the tulip stairs at the Queen's House in Greenwich, London.
They're a popular set of stairs for photographers and it's really easy to see why. Also, apparently they are one of the first unreinforced spiral stairs in the world.
Thanks as well, to the security guard who approached me when I was shooting away - "excuse me, sir" he said - here we go, I thought, and went to put my camera away. He pointed and said "there's a great angle over there you should try, they're really lovely aren't they?". Kudos to him.
Nikon D300 I Sigma 10-20mm F4-5.6