If you want to enjoy a relaxing time, in the historical heart of Warsaw, this is a place, like restaurants and bar in this neighbourhood, where you can stop. My best time of the day for this place is shorly after 6:00pm. There are enough free tablse outside and the activity on the plaza is in between (daytime visitors and night cruisers).
After a drink, you order your meal at the place but the inside of the restaurant is also worth seeing. If your are lucky (or if you book it), you might have a table on the 2 floor, by the windows. The view on the plaza is nice from this point of view.
Well, what about the food then, you have the right to ask ? Good as well. I tried the Hungarian-style pork knuckle. It was recommended on the menu. Others took the special of the day : oven-baked duck, which was delicious.