From the bottom of the Piha Hill drive past the shop and cafe towards North Piha and when you swing north parallel to the beach, park in the parking area on Marine Parade. On a busy weekend parking is available in the Piha Domain carpark next to the estuary before you reach the beach and dunes. You could also park in the carpark behind the beach at South Piha on quiet days.
Piha is an exposed west coast beach often with large waves and breaking surf. Beware of rogue larger waves surging up the beach and in around the base of Lion Rock especially on stormy days at sea. Piha Stream flows out to sea across the landward side of Lion Rock - after heavy rain it can be in flood and flowing rapidly and crossing it should not be attempted. At normal flow levels you will get you ankles wet wading across it but little more - especially easier when the tide is lower.
Lion Rock has steep-vertical cliffs around it with crumbly rock - do NOT attempt to climb up or down any cliffs. Do not linger near the base of any cliffs, especially any that look crumbly or any that may have people up above. There is a tourist track climbing part way up Lion Rock for the view. If you do climb this, do not leave the track nor attempt to ascend the last dangerous climb to the top, even if you see others doing so.
Visit best at 2 hours either side of low tide but some things can be seen at higher tides or from a distance at high tide. Walk across the beach to the bottom of Lion Rock and look at the clean rock faces at high tide level and just above, from the sand. Nothing extra to see by clambering around the rocks towards the ocean side and this can be dangerous in big seas.