This postcard of the Holy Spirit Cathedral in Belarus is from the "Legends of Old Minsk" series. The postcrosser who sent it kindly translated the card (the back gives all sorts of historical information) and she mentions that the most valuable treasure of the church is an icon of the Mother of God. It is said to be miraculous. You can see the icon here. The cathedral dates from the mid-17th century.
I don't think I've seen this stamp before. It looks a bit like a fortress. A quick search didn't net any better information, but it looks like an interesting building.
Postcrossing card #96