Mac's Track leads from the loop road above Waikopu Bay down to the coast. It was gifted to the public by former Waikopu Bay residents Mac MacArthur and Judy Voullaire, both of whom were active in politics on Waiheke for many years. It is a moderately steep walk of about 10-15 mins.
Not many people know this, but there is one of the Auckland City parks barbecues at the bottom of this track. When you get to the beach, turn left and walk along the beach about 100m and lo and behold, a clearing with a bbq in it. Free of course, but make sure you've brought everything you need, as the walk back up the hill is a bugger.