Linking Tuamarina to Picton at the top of the Marlborough Sounds, Port Underwood Road is a scenic coastal run that climbs high for panoramic views before dropping down into each bay along the way. Expect a roughly 50/50 mix of sealed tarmac and gravel, with the surface shifting between smooth dirt stretches and the occasional corrugated corner. It's an easy-going route for most vehicles when you take it steady, with plenty of bays and beaches worth pulling into for a closer look. The standout here is the scenery: sweeping outlooks over the Sounds and the chance to get right down to the water at each cove. Take care on the narrow, blind, twisty corners where passing oncoming traffic can be tight, and note that trade utes and vans sometimes travel through at speed. If you're keen to keep exploring, Tumbledown Bay Road continues on from here and gets very narrow in places. A rewarding drive for anyone passing through, ideally combined with an overnight stay in the bays.