What Sondheim did for Bernstein

Speaking of unverified web anecdotes, Sondheim Factoids claims:

He invented an elaborate game for Leonard Bernstein's 50th Birthday called The Great Conductor Hunt.

I'm thinking if I ever have a free moment (ha!), I may want to sit down and write Mr. Sondheim a letter (on real paper!) and ask more about the history of these hunts of his.