Joley B.
Yelp
A very nice national park not far from the capital. Kampinoski is huge, and warrants repeated visits in order to fully explore the park.
I was there recently for a quiet, late winter hike. The trails are well marked, well kept, and generally accessible for a variety of activities including: hiking, nordic walking, biking, snowshoeing, and cross-country skiing.
The area is generally low-land, with a few hills in spots. It makes for easy hiking - great for long distance hikes without a lot of challenge. The only down side to this flat land is that trails are wet. Even on a cooler day, with some snow still on the ground, I encountered a lot of puddles and some flooded areas. The yellow trail to Truskaw was reportedly impassible in just trail shoes according to a fellow park visitor. I haven't visited in the spring, but I imagine all this water means lots of insects come warmer temperatures.
Kampinoski is definitely worth a trip, and with its proximity to the city, it makes for an easy get away location.
If you're using public transport, be sure to check the bus schedules because only a few buses (zone 2) go out to this area from the metropolitan area.