Hi Sayhello!
We had an amazing time, and combined some off the beaten path activities with the regular tourist stops.
In Paris, we saw the Louvre, the Eiffel Tower, visited the lovely Christmas markets, went to the Musee D'Orsay, Notre Dame, and walked everywhere (in the freezing cold). We also had a great lunch at the Brasserie Boujolais (run by the same chef who runs one of Paris's best restaurants), a once in a lifetime lunch at Le Grand Vefour (one of Paris's best and oldest restaurants), and tea at Laduree, a lovely cafe (home of spectacular croissant such as chocolate/pistachio -- both in one croissant!, and outrageous macarons). We had the good fortune to go with our friends on a private tour of Paris' haute couture areas, including Chanel, and visit an atelier (workshop) that makes silk flowers. My girls took a pastry making class, but it wasn't as well designed as when Disney arranges for that kind of thing.
In London, we stayed at a very convenient and lovely hotel right in Leicester Square. We saw Les Miserables and then, for contrast, Legally Blonde. We took a private van Harry Potter tour of London, which was great fun. We walked past all the sights from Trafalgar Square past Big Ben and Parliament and across to the London Eye, which of course we rode (flew?). We also toured the Tower of London (very interesting - because it was so cold we didn't spend as much time there as I would have liked, but the lines for the crown jewels were nonexistent, which was nice). Finally we went through Madame Toussauds - perhaps the most interesting part of which was the display describing how Madame T. herself got her start and developed her business.
The biggest disappointment was that we were supposed to go to Oxford, but our train left Paddington Station and then returned to it just 30 minutes later; there had been an accident on the track on the way to Oxford and trains were cancelled for at least 3-4 hours, so we weren't able to go.
Have you taken the Eurostar between Paris and London? It was a pleasure and easy to navigate. But the train stations were very cold!
That's all I can think of right now - happy to answer any and all questions.
When (and where) is your next trip?