The most obvious illusion is that caused by the clashing colours. You could be forgiven for believing that you can see curves but there are no curves, only triangles. Technically, these are called baravelle spirals.
This is a very easy afghan to make. It is entirely in garter stitch and is worked in blocks which are then stitched together. This makes it a very portable project. You can use any yarn of your choice.
The afghan in the photo used Aran yarns and is approximately 110 cm x 160 cm (44 inches x 63 inches). You can use any yarn though this might change the overall size.
The pattern includes a colouring sheet so you can try out your own colour choices.