Looks like you have seen more than me! I'm glad you mentioned museums and galleries, the Natural History Museum and the National Gallery are, in a word, impressive and I love visiting these when I am in London. Only a year left....how are you going to choose what to see next? The choices appear endless. There are places I have been but not always on the grand scale as Durham Cathedral or Westminster Abbey; I quite like to visit the smaller places that sometimes get overlooked, however, I would like to see Petworth House, Chatsworth, Knole, Alnwick Castle, Conwy, Caernafon Castle, Chartwell etc. the list goes on and on. There's simply so many places I haven't seen and still want to.I enjoyed Leeds Castle, Apsley House (No. 1 London, the Duke of Wellington's residence, which was smaller than I thought but impressive all the same), Scotney Castle, Bateman's (Rudyard Kipling's Jacobean home and even the first property ever given to the Nation Trust, Alfriston Clergy House. I just like visiting history buildings and ruins and if I could afford it I would take time off work and travel to see them. There is a book called the Treasures of Britain, which has incredible selection of beautiful photos along with informative descriptions of just about all the best places to see in Britain. If you use this book for anything, use it to remind you of the places you have been and the places you still want to see when you plan your next trip back to the UK. My copy was a lot cheaper than shown on Amazon so I know you can get them at a lower price.