Two of the easier other choices would be London or Madrid. From Amsterdam you can take a train to Brussels and then change for the Eurostar train to London, or you can fly. From London to Barcelona you’d want to fly for sure. If you chose Madrid you can go to Amsterdam and then fly to Barcelona and then take a train from Barcelona to Madrid in only 2.5 hours.
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.