Unusual things...may or may not be your taste.
Leeds Castle, or another....Hedge Maze preferred for the kids.
Victoria and Albert Museum. Stuff there no where else.
Catacombs, or Roman Ruins in London.
Underground tours of Paris
Novelty Automation in London, fun.
Covent Gardens, shopping, London
Kew Gardens. Superb.
Eat daily specials in Local Pubs.