Conversation so far:
What was the Mirror challenge?
challenged Houdini to escape from special handcuffs that it claimed had taken Nathaniel Hart.
Who challenged Houdini?
London Daily Mirror newspaper.
Who was Nathaniel Hart?
a locksmith from Birmingham.
What was special about the handcuffs?
five years to make.
When did he complete the challenge?
March 17.

Question: Where did he do it?
Self-contained rewrite: Where did Harry Houdini do the mirror challenge?