Varenna, on the eastern shore of the lake, can be visited easily from Bellagio by either the car ferry or the passenger service. A return ticket costs €9.20.
I found it a more attractive town than Cadenabbia as the main road is higher up and does not come through the centre of the town. There is a very pleasant walkway along the lake side between the ferry pier and the town centre.
The gardens of the Villa Monastero are worth visiting.
Varenna is a gorgeous fishing village below the castle of Vezio, the famous home of Teodolinda the Lombard queen. Other attractions to see in this village are Villa Monastero and Villa Cipressi. The ferry departs from Bellagio wharf on a daily basis, the timetables can be found on the board next to the wharf.
Situated next to Villa Monastero, this is also well worth the couple of Euros it costs to wander through the gardens. Both gardens exhibit (well-labelled) botanical specimens in a beautiful landscaped garden.
Just a short ferry ride from Bellagio, is the small town of Varenna which is home to Villa Monastero, Villa Cipressi and Castel Vezio. You can't go inside the villas but for a few Euro you can walk through the gardens, trying not to take too many photos which is hard to resist in such beautiful suuroundings.