On a hot day there is nothing better to do in London then go for a swim in the Heath ponds. You get completely transported you out of the city as Hampstead feels like being in the countryside except you're in central London?!
London has great green spaces. There are large royal parks and small public gardens, hidden allotments and roof terraces. Each one has its own identity and characteristics and everyone has their favourite. In summer they become extensions of people homes, you see girls sunbathing from 9 am and the endless picnics mean you can eat 3 meals a day in the park. My favourites - St James Piccadilly Gardens, Hyde Park, Barbican Conservatory.
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.