Die Hel is a famous pool in the Groot Winterhoek mountains (not to be confused with De Hel near Oudsthoorn). It is the biggest and best rock pool in the Western Cape, surrounded by cliffs and a large waterfall. It's about a 15km hike to this point, so you should plan to camp out or spend the night at De Tronk or another hut in the area.
Although many people hike to Die Hel, few go down the Twenty-four Rivers kloof which ends in this pool. The kloofing trip begins at the road bridge which you cross just before you get to De Tronk. (Above the bridge is the Klein Kliphuis River, also a pleasant half-day kloofing trip.) In many places you can clamber between and under the boulders of the kloof, wading and swimming through caverns and tunnels between the boulders. Your trip ends spectacularly at Die Hel, where the only way you can get down to the pool is a jump of about 5m.
After the jump there is a steep climb out of the gorge , but the view and sense of achievement are well worth it.