Conversation so far:
How did the Vienna Boys' Chior get started?
The Vienna Boys' Choir was, for practical purposes, established by a letter from Emperor Maximilian I of the Holy Roman Empire on 30 June 1498.
Who was the singing master of the Vienna Boys' Chior?
The singing master of the Vienna Boys' Choir was Jurij Slatkonja.

Question: Where did they sing?
Self-contained rewrite: Where did the Vienna Boys' Chior sing?