This is the day to do first. In forty miles it takes in a lighthouse you can walk to across a golf links, one of the great houses of Scotland, a beach, an optical illusion that has baffled people for a century, and a free clifftop castle with a very dark story — and it does it along the A719, which is the finest stretch of road on this coast.
The route runs north from Girvan and comes back the same way, so you can shorten it at any point without ruining the day. With small children, cut the lighthouse walk and give the time to Culzean's playgrounds instead.
Notes on the stops
Turnberry lighthouse stands on the site of Turnberry Castle, a plausible birthplace of Robert the Bruce, and you reach it on a path across the championship links. Keep to the marked route, watch for golf, and give way to players.
Culzean is the anchor of the day and deserves at least three hours. The Robert Adam house has the famous oval staircase and the Eisenhower apartment; outside there are 600 acres of country park, a walled garden, the Swan Pond, two adventure playgrounds and a beach below the cliffs. The castle interior is seasonal and the country park is open year-round. Entry is paid, and free to National Trust for Scotland members.
The Electric Brae takes five minutes and costs nothing. Stop in the marked lay-by, take the handbrake off, and watch the car apparently roll uphill. It is an illusion created by the lie of the land, and it works every time.
Croy Shore below the brae is a long quiet beach, excellent for rock pools at low tide and usually near-empty.
Dunure finishes the day: a free castle ruin on the rocks, a small harbour, a play park and turf labyrinth at Kennedy Park, and a café and pub for tea. The castle is where the 4th Earl of Cassillis roasted the Commendator of Crossraguel over a fire in 1570 to make him sign over the abbey lands — a story children find extremely satisfying.
Practical notes
Culzean is the only paid entry on the route, and the only place you need to think about opening times. Everything else is open access. Parking is free at Maidens, the Electric Brae lay-by, Croy Shore and Dunure's Kennedy Park.
Fuel and shops in Maidens and Dunure are limited — Girvan and Maybole are the reliable stops. The A719 is narrow and busy with cyclists on summer weekends, so take it slowly, which is the point anyway. Coming home, the A77 takes half an hour from Dunure, or you can retrace the coast road for the sunset over Arran.