Castelldefels is where Barcelona goes to the beach, and where the coast suddenly stops being flat. Behind the town's long sandy shore, the limestone hills of the Garraf massif rise abruptly, and just south of town the coast road begins its famous run along the cliffs to Sitges. A castle on a small hill, rebuilt many times, gives the town its name and keeps watch over the plain of the Llobregat delta to the north.
The beach is the heart of the place, several kilometres of fine sand with chiringuitos, beach bars, and a lively crowd in summer, when kitesurfers fill the water on breezy days. Planes from Barcelona's airport pass low overhead as they climb out over the sea. Away from the beach, Castelldefels is a prosperous residential town, popular with the wealthy, including many of Barcelona's footballers.
The road to know is the C-31 south toward Sitges. Once past the last houses, it clings to the cliffs above the sea, through tunnels and around a series of tight, blind bends, with views straight down into the coves and over the water. It is narrow and busy at weekends, with cyclists and cars, and police watch it closely, so ride it calmly and enjoy the scenery rather than chasing a time. Inland, small roads climb into the Garraf Natural Park, a dry landscape of scrub, limestone and pine where you can find a Tibetan Buddhist monastery among the hills, and the Modernista wine cellars at Garraf, designed by Gaudí, stand beside the coast road.
The rides from here go in very different directions. The Priorat ride heads southwest along the coast and inland to the slate vineyards and mountain villages behind Tarragona, while the Cap de Creus ride runs northeast past Barcelona to the rocky peninsula near the French border, where the Pyrenees meet the sea and Dalí made his home at Portlligat.
Castelldefels has everything: fuel, supermarkets, cafes and restaurants, many serving paella and seafood on the beachfront. Traffic on the C-32 motorway and around the town can be heavy in summer and at rush hour, and parking near the beach in July and August is a challenge, though bikes usually have more options. For the best of the coast road, go early in the morning, when the light is soft and the traffic is still asleep.