SH73 swings from the Taramakau River valley into the Otira River valley. About 4 kms in, you will see the Morrison Footbridge. You get great views up and down the valley from this bridge. It is also the southern end of the Harper Pass section of Te Araroa, which connects back to the Lewis Pass Road near Lake Sumner.
Continue on to the hamlet of Otira at the base of the climb up to Arthurs Pass. The Otira Hotel is a must stop; in addition to the external Lord Of The Rings models, it has a great collection of historical items and a history of the area on its interior walls.
From the hamlet, the windy climb up the gorge to the Pass begins. There are a couple places where it is safe to stop for a photo.
The best time to do this drive is winter, with snow on the mountain peaks, or mid-January when the rātā trees along the valley flower. Rātā is similar to pōhutukawa, and the massed presence of red in the Otira valley amongst the green forest is stunning.