zoliborz i s a district where you can find loads of parks, housing estates that hide some beautiful buildings like 'Komedia' theatre (which is a rather thrashy theatre) and small coffee houses and clubs/pubs. 'Sady Żoliborskie' is a part of district where years ago was a big orchard. Now it is housing estate, but still it has some of the orchard atmosphere - great place to take a walk. Warsaw is full of flats hidden by high fences - Żoliborz is still defending itself from this - it makes you walk everywhere, so tramping is not confusing. you should check two pubs/clubs - 'Pracownia' and 'Małe tęsknoty' - you can find here some nice, alternative concerts. They are situated under small flats, in the cellar.   

Zoliborz - a beautiful old part of Warsaw with many houses built in '20s... a lot of parks and places to hide within the big city... very important in the whole history of this place... really beautiful and worth of visiting!!!!!!!!

One of the most charming districts of Warsaw - even where the construction dates back to 1960s...

Try Google translating http://pl.wikipedia.org/wiki/%C5%BBoliborz - much more detailed than the English version.

best district!
green, nice and my favourite :)