My two favorite hobbies these days are collecting Nancy Drew books and letterboxing! Here are some clues that involve the intersection of these two hobbies.
#19 The Quest of the Missing Map (gone missing)
#40 The Moonstone Castle Mystery (currently missing - may be replaced soon)
#122 The Message in the Haunted Mansion
Edward Stratemeyer (individual credited with creating the idea for the character of Nancy Drew)
Harriet Statemeyer Adams (individual who ran the Stratemeyer Syndicate that produced Nancy Drew books for 50 years) - COMING SOON