First, you punch two holes in the front.
Then cut the laces once in the middle.
Now you thread a shoelace from the inside to the outside through both holes. Make sure that you use the pressed lace of the shoelaces to thread through.
Then knot the cut-off end inside the cardboard box.
Now you put a small loop and knot it in the inside of the box as well.
Now cut off the remaining laces.
Only the loop is visible on the outside of the carton.
Now you open the lid of the box and punch two holes in it.
Also thread the shoelace from the inside to the outside, place a loop and knot the ends on the inside. Make sure that the loops are so large that you can connect them to the lock.
Now you can attach the castle and close the treasure chest.
Design your treasure chest as you like it and surely you already have treasures that you may hide in it.
Have fun!