We reccomend go to the walk especially it will be the beginning of spring. Łazienki Królewskie it’s not only a green park,  but also  place full of historical objects,  for example:Palace on the Island, White House, Myślewicki Palace, Old Orangery and much more…
More information: http://www.warsawtour.pl/en/tourist-attractions/azienki-kr-lewskie-museum-muzeum-azienki-kr-lewskie-3347.html
We reccomend:
– If you’re going to the Old Town you can visit viewpoint in Bell Tower at St. Anna’s Church on Krakowske Przedmieście street.
You can look at the Old Town from a different point of view.
Opening hours in April: 10:00 – 18:00
-If you are in Warsaw you can’t miss the Palace of Culture and Science.
Go on the 30th floor and enjoy the wonderful view of the whole city.
Opening hours in April: 09:00 – 18:00
Exept the obvious choices like the National Museum or the Warsaw Rising Museum we reccomend POLIN Museum of the History of Polish Jews.  This museum is open from 2014 and is dedicated to the 1,000 years of shared history of Jews and Poles.. You should also visit the museum because of the very interesting architecture. We will be in the center of Warsaw, everyone will surely find something for themselves between dances.