The start of the Ou Wapad trail is located on Ou Kaapse Weg near Silvermine Village. There is only space for about 4 or 5 cars at the trail entrance, so best to get there early, otherwise you'll need to park a little further down the road.
The trail is a very well maintained gravel jeep track and also a favourite amongst mountain bikers, so keep a watchful eye out for them during your walk.
The Ou Wapad runs nearly parallel to Ou Kaapse Weg all the way up to the Slivermine West entrance, so as you walk up the side of the mountain, you experience the unusual sensation of feeling completely removed from civilization - but every now and again will hear and see cars coming down the mountain. While walking the trail you get to experience beautiful views of the mountain, Fish Hoek and Noordhoek beach.
Due to the 2015 fires the fynbos vegetation has been burnt back quite aggressively and while the vegetation is recovering there is very little shade on the trail, so be sure to take your hat and ample water. There are also a number of trails (like the River Walk) that split from the Ou Wapad, but they remain closed due to the fires.
You can either leave a car at the Silvermine West parking area and drive back to the starting point or simply turn around and walk back down the mountain. One way the trail is just a shade short of 5 km and takes just over an hour to walk with about a 200m height gain over the duration of the walk.
Check out the trail map here: http://planethike.com/gps-tools/viewtrack/6-ou-wapad.html