Well worth a day trip, meander along from Mackers, via Sabie and Graskop - 35kms north of Graskop are the Potholes. Follow the R532.
This is an extremely well presented attraction that is well worth a lengthy stop. There are nice picnic areas and the walk around the potholes is excellent - this is one of the world's largest canyons. Be sure to take your hiking shoes.