This has to be our favorite genus right now. Astrophytum are incredible little cacti native to parts of Mexico and are known for their odd shapes and variety within the genus. They have adorable flowers that occasionally form at the head of the cactus almost looking like a little crown or hat. They are notoriously slow growers but as they mature they swell and swell and can reach about 1ft tall. We discovered last winter here in Portland they are cold hardy outside up to 25 degrees which is pretty impressive. Though this makes sense in their native habitat they will reach incredible temperatures during the day and freezing temps at night.
We recommend bright light even direct and watering only every 4 weeks or so. In the summer you may find it'll need more water around every 3 weeks. They thrive in super coarse mixes.