One of the things I liked most about San Francisco were all the residential houses. They weren't all that big and were painted a large variety of colours. It was also interesting to see how each house had coped with being built on the side of a hill.
All the houses were so densely packed together and when standing on one side of the valley looking across it was really possible to get a sense of the size and steepness San Francisco is built on. It was never fun to stand on one side only to realise you needed to be at the top of the other!
Canon 400D, EFS 17 - 85mm f4 - 5.6; 85mm, f16, 1/30, ISO 100