I'm a big fan of Richard Serra. As this is the train station I use to pass in and out of London. I think it's safe to say i've spent more time gazing and contemplating this art work than any other on earth! The steel monolith sits in a rather petite amphitheatre with surrounding step/seats. During the week, it's packed with picnicking stray commuters. I just love sitting there.
My friend Guillaume opened the swankiest rooftop in London that still feels like a house party. Louie is a French-Creole restaurant, live jazz music venue and oyster bar too.
Maybe an obvious choice, but the Barbican is always good. My favourite space in there is the curve gallery, last time I went was for Cory Arcangel's 'Beat the Champ'. I love the architecture, although not many people do. I think it was voted 'London's ugliest building' in 2003.