Watercolour cards always have a unique charm, I'd say :) This one in particular depicts Nesvizc Castle, located in Belarus. It's a a residential castle of the Radziwiłł family, an old noble family of Lithuanian origin. You can learn much more about this interesting family here. The estate has been owned by the Radziwiłł family since the middle ages and even the Lithuanian Archive was moved there. What an influential family! In 1994, the castle complex was designated the national historical and cultural reserve. In 2005 the castle complex was listed by UNESCO as a World Heritage Site as well.
Many thanks to Maria for beautiful postcard and even nicer stamps!