The Altarpiece of Veit Stoss (also St. Mary's Altar), is the largest Gothic altarpiece in the World and a national treasure of Poland. The altarpiece is located inside St. Mary's Basilica, a Catholic Church adjacent to the Main Market Square.
The Church of Spilt Blood, Saint Petersburg, Russia. Russia is underrated in my opinion for its amazing architecture. Synagogues, Mosque, and Cathedrals have always drawn my attention. The colors and style of this is absolutely stunning.