I transited twice through London when I was in America. I didn't get chance to see London even from Bird's eye view but 2011 trip to USA gave me chance to see London from top and had some fulfillment since can easily watch Themes river, London bridge and London Eye.
First trip to London was remembered because of endless walking on the banks of Themes. In my first trip, I started walking from Westminster Abey to London Bridge which covered iconic London eye. But walking always give fulfilling experience since on the way you can see many things.
During my short stay, I also had to visit French embassy for European visa and it was close to Kingston garden, so liked it very much.
Also visited Greenwich area and apart from historical astronomical observatory. It has maritime museum. But most I liked was painted hall at Old Royal Naval College.
To go to Greenwich, you have to pass modern London. i.e. Canary Wharf. You come across many modern buildings at this place. Also station is on modern train line - DLR line (Docklands Light Railway - metro)
Visiting Winsor Castle was like almost visiting lost glory of British empire. There was a huge queueto entry and people were from all over the world. Palace itself is magnificent. No wonder queen ruled from here.The original castle was built in the 11th century after the Norman invasion by William the Conqueror. Since the time of Henry I, it has been used by succeeding monarchs (39) and is the longest-occupied palace in Europe.The castle's lavish, gothic in architecture. State Apartments today reflects the changing tastes of the Castle’s royal occupants, particularly Charles II (r.1660-85) and George IV (r.1820-30). The State Apartments, particularly St George’s Hall and the Grand Reception Room are beautiful.
You have to visit, Lloyds Cricket Ground if you are Indian and love cricket. One fine weekend, I went to see Lloyds and it is historical place. I liked their guided tour to pavilion which include showing ashes urn, Long room, Dressing room, Honours board and JP Morgan Media center.