Many of the tents we sell have a thick, durable groundsheet built-in so you would not need to buy an additional one. There are some of our bigger tents that offer a separate groundsheet for those times you are camping on wet or rocky ground.
Please note: Any of the Crua Cullas ***can*** be used on their own, but they were designed to work inside of water/weather resistant outer tent (like the Duo, Duo Maxx, or other).  If you choose to use one of the Crua Culla tents on their own, then you would need to suitably protect it with a groundsheet and a tarp as this tent is not waterproof.