The PCH north out of Santa Monica is one of the great drives, and most people do it badly — straight up and straight back with no stops.
The stops that are worth it
Getty Villa. Roman antiquities in a reconstructed villa above the sea. Free, but timed entry — book ahead.
El Matador State Beach. Sea stacks, caves, a steep staircase down. The most photographed beach in Malibu for good reason.
Point Dume. A short climb to a headland with the whole coastline either side. Whales in winter and spring.
Malibu Pier and the Country Mart for lunch, if you want somewhere to sit.
Timing
Go in the morning. The afternoon marine layer can grey out the whole coast, and the PCH back into Santa Monica on a summer evening is slow.
Why not to drive it yourself
The good bits are on the left going north and there is nowhere to stop quickly. Parking at El Matador is a small cliffside lot that fills. Being driven means you look at the sea rather than the car in front.