A place that really grows on you, with each visit the Barbican reveals more of itself to you and your bond is tightened. The Barbican Kitchen is great for coffee or lunch, summer hangouts by the ponds, cinema in winter, the amazing Barbican Hall for live music, and don't miss the conservatory.
Warm summer nights should be spent in the high grass in Hampstead Heath above the ponds. For midsummer bring herring, snaps and songs and stay until sunrise!
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.
The Thai food scene in London is in an incredible place right now, with the likes of The Smoking Goat, Som Saa, The Begging Bowl and Farang all offering an experimental and delicious take on the cuisine. I'm focusing on the later a) because it's my local and b) because it's helmed by Seb Holmes, who's also cheffed at those others mentioned, and has managed to bring the best of all of them to Farang. Oh and c) the Gai Prik is probably the tastiest dish in London