Rotterdam is an easy day trip from Amsterdam by train. There are local and express trains running into Rotterdam Central Station. The city was heavily bombed during WWII, so has a much more contemporary feel than Amsterdam or The Hague. You will see some great contemporary architecture including the beautiful Erasmusbrug Bridge connecting the North and South parts of the city and the Cube Houses by architect Piet Blom across from the Markthal.
Kunsthal Museum: Museumpark Westzeedijk 341. With a focus on contemporary art, the museum hosts close to 25 new exhibitions during the year covering all kids of cultural expressions. Though the building is a little confusing to navigate, make sure to check out the current schedule.
Museum Boijmans Von Beuningen: Museumpark 18-20. This museum has an extensive collection of over 140,000 pieces consisting of old masters, modern art and design. You will see some great works by Rembrandt, Rubens, Van Gogh, Frans Hals, Jan Steen, Kandinsky, Magritte, Dali, Leonardo da Vinci, Max Beckman and many more.
Markthal: Not to be missed, is this recently opened market and food court. I went to Rotterdam mainly due to the articles I had read and the pictures I had seen. It is a wonderful curved building with a painted ceiling of large flowers. It is part of a building that has a number of apartments along the side and across the top. Here you will find sellers of cheeses, vegetables, meats, pastries, flowers and fruits and vegetables. Along the sides are a diverse selection of restaurants to try. I enjoyed a tapas restaurant with a local friend.