Catch the train from Genova Brignole station to Santa Margherita Ligure (about a 30-minute ride, leaving every ~30 minutes) and walk down to the large dockside pedestrian area. You will see the bike rental station just a few steps away from the bus ticket kiosk. For ~5 euros, you can have a bike for the whole day—a perfect option for exploring the fantastic surroundings!
While the roads are all paved, they are incredibly narrow, and cars tend to drive quickly. Just be aware and stay very close to the edge for your own safety.
Portofino (a 15-minute ride) is a gorgeous town frequented by international tourists and stunning yachts in the summer months. Originally named for the schools of dolphins (Port'Delfino) that often pass this cove, the landscape around the village is breathtaking. If you come in the spring, you can ditch your bike to spend the day hiking the paths up to the perched fort and church, or simply enjoy a gelato while gazing at the quaint fishing boats in the marina.