The best thing about Paris,,, well, too many things to single out one,, but the food, the wine, and the "cafe culture".. I love stopping for a long lunch.. people watching,, munching away at a delish cheese plate,, sipping some wine.. ahh.
London,, the best thing for me,, so far,, Museums and Art Galleries,, many happy afternoons can be passed in the numerous and amazing Musuems( love Victoria and Alberts, and the Portrait Gallery)
Rome- History,, being in St Peters,, visiting the Forums.. the Colesuem... etc.
Greece- the islands,, if you can't enjoy the Greek islands,, well,, I can't imagine you enjoy life
Switzerland and Austria- any small town in the Alps,, my goodness,, they DO look like postcards,, perfect chalets,, amazing snow covered peaks, great hiking trails.. and cheese fondue!