Amsterdam is fascinating - a true gem among gems in northern Europe. Dutch architecture is on prominent display: think 17th-century canal houses with modern, open interiors, then a houseboat directly underneath, on one of the four main canals. Residents are friendly, creative and authentic to a high degree. Yes, that's Amsterdam.
Some estimates suggest there are more bikes than people in Amsterdam, and the city streets pulse via two wheels, not four. Case in point: Dutch politicians are pushing for a ban on non-electric car sales by 2025. One of many reasons making the nation one of the most progressive and happiest places in the world, according to virtually every study published on the topic.
While 48 hours just scratches the surface of the beautiful city, the timeframe isn't too unrealistic - Amsterdam Schiphol has the most non-stop destinations in Europe, meaning an extended layover can be easily achieved before heading onward.
There's also multiple points options to get you there from the west coast and east coast of the United States. I recommend stocking up on United miles for either a Lufthansa flight via Frankfurt (on an A380 double-decker plane) or Swiss Air via Zurich. 140k points books you a seat in business - half of that in economy, assuming you book well in advance.
Finally, I highly recommend racking up InterContinental points for the absolutely stunning InterContinental Amstel Amsterdam. The atmosphere is elegant; the furnishings are comfortable. Chase has a credit card that works, and Ultimate Rewards points transfer. The Waldorf Astoria is a good hotel to pair, if using points, or the recently opened Andaz.