Step 1: Square base
02.Apply two vertical valley-folds of the step #1.Prepare to unfold two valley-folds.
Step 2: Inside reverse-folds
04.Apply two valley-fold of the step #3.Prepare to open the front-most layer following the arrow
Step 3: Inside reverse-fold
06. Apply the "inside reverse-fold" of the step #5.Prepare to close it.
Step 4: Front-most layer
08.Open the front-most layer.Prepare to apply an "inside reverse-fold" .
Step 5: Start for 5 step
10.Close the flap.Prepare to turn the model over.
Step 6: Start for 6 step
12.Repeat the steps #1-10.Prepare to apply a horizontal valley-fold.
Step 7: 7
14.Apply the vertical valley-fold of the step #13.Prepare to turn the model over.
Step 8: 8
16.Apply the horizontal valley-fold of the step #15.Prepare to apply a vertical valley-fold.
Step 9: 9
18.Apply two valley-folds of the step #17.Prepare to apply a valley-fold and then unfold
Step 10: 10
20.The crease patter of "open sink-fold" of the step #19 is shown here.