Question: What is the name of the town square that is on the border of the first and fourth districts of Vienna and one of the most frequented and best connected transportation hubs in Vienna, the location of Karlskirche which is  widely considered the most outstanding baroque church in Vienna?
Sentence (from "Karlskirche"): Widely considered the most outstanding baroque church in Vienna, as well as one of the city's greatest buildings, Karlskirche is dedicated to Saint Charles Borromeo, one of the great counter-reformers of the sixteenth century.
Relevant evidence: Yes