Did you know that in the 17th century they didn't have envelopes at all? Letters were skillfully folded in a variety of ways so that the message was protected from weather, wind and prying eyes! Learn letter art from the 17th century: write or draw with a quill; then beautifully fold the letter and seal it with a wax seal. Just like Johan de Witt did! By the way, this is not all: Johan often used secret writing. He invented all kinds of codes himself.
Get inspired and write or draw a top secret letter, unreadable to friends, girlfriends, grandparents, grandparents and perhaps most importantly, your parents.