The crazy-cheap roundtrip fares, which were spotted by the crack team at Scott's Cheap Flights, are available for a number of flights to over a dozen popular western European destinations, including Amsterdam, Bologna, Bordeaux, Dublin, Lyon, Marseille, Milan, Naples, Nice, Paris, Rome, Rotterdam, Toulouse, and Venice. Better yet, you can nab a good deal from nearly every major airport in the contiguous US. They're also available on a number of major airlines, including both budget and mainstream carriers.
As of this writing, there were still lots of wildly affordable flights available from most departure cities between now and May of 2018 according to a preliminary Google Flights search. However, there are some particularly super-cheap standouts like a $269 nonstop flight from Dallas to Milan on American in April, a $350 nonstop from New York to Rome on Norwegian February, and $380 flights on WOW Air from Chicago to Amsterdam in May. It may take a bit of back and forth plugging in different departure and arrival cities, but odds are you can find a great fare from somewhere near you.