This is a really stunning card and I'm afraid my scan doesn't do it justice. This is the Palace of Culture And Science in Warsaw, which was built in 1955. It's a controversial building as it was a gift from the USSR to the Polish people and was dedicated to Josef Stalin. It dominates the city skyline (many think it ruins the aesthetic balance between old and new town in the city).
It looks like a massive structure and is the largest building in Poland and the eighth largest in the European Union. It has an exhibition center, office complex, as well as theaters, cinemas, museums, offices, bookshops and a conference hall.
The stamp on the left commemorates Sieradz Cathedral located in the city of the same name. I'm afraid I've not found any information on the second stamp, only that it is a manor house, Dwor w Janowcu Pulaw.
My first card and stamps from Poland!