From December through February there are literally no European cities that could qualify as having “great weather,” except for the Canary Islands, which is listed below. So during the winter Europe is all about cultural tourism, and lower hotel prices make it especially appealing for those who like to stretch their travel budgets and avoid crowds at the same time.
Just came back from Luang Prabang, Laos. Cheap and easy to navigate. If with kids you can do an elephant training camp few days. Airport 15 min from hotels and just 2 minutes to get visa (30USD). Not so much to see, but nice vibe and cheap. If you have to choose between Luang Prabang and Siem Reap, Siem Reap has more to offer, but is much hotter than LP in December.
Traveling during the last ten days of December means crowds and exorbitant prices throughout much of the world, but the first two-thirds of the month—before holiday airfares and hotel rates go into effect—can be a serene, value-laden, and just plain lovely time to vacation. Europe is all decked out for the holidays—with locals generally friendly and in high spirits; in the Southern Hemisphere, spring is in bloom; and in the Caribbean, Hawaii, and Mexico, hurricane season is over, the weather is gorgeous, and there are free upgrades galore.