This magical chasm is definitely worth a quick stop as you're driving through the Haast area.
Although it's only a couple minutes walk, be prepared to get your legs wet as you need to cross the water to walk into the canyon. The water is freezing cold so I recommend taking some water shoes or sandals. Do not attempt to enter the cayon during or after heavy rain.
To find Wilsons Creek Chasm, head towards Fantail Falls in Haast Pass. Just before you reach the falls (if you're driving from Wanaka) you'll come across a small bridge (there's a tiny white sign which says Wilsons Creek on the left side). There is a pull over spot just before the bridge and another just after the bridge, park in either spot and cross the road to reach the bridge. You'll then need to climb down the rocks on the left side of the bridge (if you're facing it stright on) and cross over the small river to make your way into the chasm.
Extra info:
Distance: Approx 100m
Walk time: under 5 mins