We spent four days in Paris the weekend between Christmas and New Year’s. It was beautiful, not very busy, and cold.
The Eiffel Tower: worth climbing to the second floor for sure. The line for the stairs was much shorter than the elevator, so we took the stairs. There’s no choice but to take an elevator further up if you wish to go to the top. We did. No regrets, but it’s not really necessary, either. The second floor is impressive on its own.
Versailles was even more ornate than I expected. I’d like to visit in the spring or summer to see the gardens. I booked my tickets in advance, which meant I was able to spend 5 minutes in the queue rather than an hour (said queue is surely much worse in warm weather), but the really pro way to see Versailles is book a tour in your language. That lets you enter with your tour group, and then you can stay inside the gates and view the rest of the palace on your own without needing to back out to the queue. You need tickets to enter whether you do the tour or not, but the tour is worthwhile in its own right, and the ability to skip the queue is a nice bonus.
The whole time I was there I couldn’t help but think about how such ridiculous excess ultimately resulted in the French Revolution.
The Louvre would be worth seeing if all the art and artifacts were removed. The building itself is gorgeous. No one does ceiling moldings like the French. Again, book your tickets in advance. The worst queue here wasn’t to enter the museum itself, it was to get through security. If you enter through the Lions’ Gate or another side entrance, you can drastically cut down the time you wait. You can also book timed tickets, which we did; we had to wait for all of five minutes.
I’m not sure if you can book Notre Dame ahead of time. If you can, and you want to see the inside, you should. We wandered around the outside and skipped the inside due to lack of time for the queue. Basically, if you want to see anything in Paris, book ahead of time.
Also, research your restaurants in advance. We picked a random spot for our first meal just because it was near our hotel. I will charitably call it mediocre and accurately call it over-priced. I spent an extra ten minutes looking for food for subsequent meals with much better results.
Spend the extra ten minutes is pretty good dining advice anywhere. Download Yelp (for the US) or Trip Advisor (for Europe) and look at some reviews. See how a place rates. If it’s not in the top 10% in its city, consider something else unless you have inside info. Also look at the 1-star reviews and see if they are coherent and whether they address the same things. I’m perfectly willing to ignore bad reviews if they are reflective of staff having a bad day, but I’m less inclined to ignore them if multiple people mention quality declining over time.