Anonymous wrote:There is no way in hell to avoid crowds
The best way is to decide not to go see specific well-known sites (Mona Lisa at the Louvre). You can also stay in less touristy neighborhoods. Another tip for ports is to look at online calendars of cruise ship port calls.
There definitely are time of day effects that can be researched for various sights.
Crowded art museums aren't fun. Going 1st thing in the AM and going straight to see the most important things works pretty well. Night openings also work well.
Final tip, request a tour from a local greeter organization.