Approached from Cape Town, the most pleasing route is as follows:
Take the N1 north until you reach exit 47. Take this exit and turn left onto the R44 which you follow in the direction of Wellington (left) for 28km. Do not turn off this road. You will pass various turnoffs and crossroads, which you should bypass, until you reach a long uphill stretch, with the town of Wellington on your left. At the third robot, with the cemetery on your right, turn right and drive downhill for approximately 1km. You will see the signs to Diemersfontein on your left

GPS Co-ordinates:
WGS84: S 33 39 33.7    E 19 00 15.8
X: 19.0043889 Y: -33.6593611