The word "mandala" is from the classical Indian language of Sanskrit. Loosely translated to mean "circle," a mandala is far more than a simple shape. Mandalas are great to stitch! Fun, repetitive motifs and designs using just simple, or more advanced stitches are good for the soul and your nightly stitching therapy.
Use a single colour, a variegated, as I have done (all our mandalas were stitched with Cottage Garden Perle #12 handdyed threads) or many colours in the thread of your choice.
Use your hoop to frame them as hooped wall art, or stitch a whole collection for a quilt such as Razzadazzle.