Sestri Levante's position on the Genova–La Spezia rail line puts the best of the Ligurian coast within easy reach by train.
The Cinque Terre — the five cliff-hanging villages of Riomaggiore, Manarola, Corniglia, Vernazza, and Monterosso — are the obvious excursion, reachable in about 30 minutes by train. Go early on a weekday if you want to walk the coastal trails without sharing them with vast crowds.
Portofino is famous, expensive, and worth visiting once: the tiny harbour village perched on its peninsula is genuinely beautiful. Take the train to Santa Margherita Ligure and then the bus (15 minutes) or ferry.
Camogli is less visited than Portofino and arguably more rewarding. The tall, narrow houses stacked above the harbour, the fishing boats, and the basilica overlooking the sea are classic Ligurian. From Camogli, you can walk or take a ferry to San Fruttuoso, a medieval abbey in a remote bay accessible only by sea or on foot.