How will it get there? Take a boy, a messy bedroom, and a friend who is having a clear-out as she moves house. She gives the old trunk to the boy, and he fills it with toys and games he no longer uses: old note books, perhaps, and comics? Intrigued to have something that locks, he locks it. Several years later, as he is, himself, having a clear-out of sorts, he realises he has (a) lost the key, and (b) forgotten exactly what's in the trunk.
I'm reluctant to force open the lock: it's a beautiful old trunk. It's just possible we will move it upstairs to the storage space in the roof behind our bedroom. It will go nicely with the boxes and boxes of Lego that have recently been moved up there, boxes into which J has tucked a note to his future self: a kind of time capsule.
And there — voilà! — we will have our very own old locked trunk in the attic.