When I was around the age of 6 I went to a friends birthday party, his house was a 70's casa with beautiful carved wood double front doors. After all the gift giving and pizza eating we all headed up stairs to play football in one of the rooms(bad plan parents, bad plan.) Someone threw the football too hard and it hit the bookcase and what do you know, THE BOOKCASE OPENED! I swear its true! Behind it was a little storage room filled with many, many artificial Christmas tree's.
I can only say having an experience like this at six sparks your imagination! From then on I have loved the idea of a secret room, I went around tapping all the walls when we moved to a new house at seven, Clue was my favorite movie for years.
Here are a couple photos to spark your imagination!
The best part about secret passages is they do not have to be elaborate, ingenious or expensive. Hollow out a floorboard or hide your money behind a picture, the point is to have fun with it and get creative(And smart too!)