My family and I are traveling to several countries in Europe beginning od December. I'd love to follow recommendations in this forum but I don't see all of the cities we'll be going to in this forum. My question is how trustworthy is using Trip Advisor for finding Day Tours or is there a better website to use? Thanks!
You can use Trip Advisor which will take you to their Viator tour division. I would recommend you LOOK there to do your research and then book directly with the provider instead of booking thru the 3rd party of Viator. Viator (and similar GetYourGuide) do not actually run the tours, they are just a middleman.
I've been astonished by how many minor towns and cities have been discussed on these Forums over the years - how are you looking for the cities in several countries?
You could try listing some of them here and you might be surprised by just knowledge is stored in our very experienced hive brain.
Welcome to the Forums
I've used the TripAdvisor "Things To Do" feature for many years with good results, both for scouting out local attractions I might otherwise have missed and for the occasional day trip provider as you've mentioned.
Have always found their user reviews to be quite trustworthy when trying to sort thru the various options.