Bastia serves as the administrative centre for the Haute-Corse region and is the second most populous town in Corsica after Ajaccio.
My suggestion
I advise you to go walking around the little streets of the Terra Vecchia district, preferably on a market day. This is where the true heart of the town is to be found. The town's squares are exceptionally lively places, and visiting them during your stay on Corsica will give you the chance to get as close as possible to the very heart and soul of the island.
The GR20 is a difficult trek that is known to walkers from all over the world. It crosses Corsica, from north to south, or the opposite, in 15 days of intensive walking. But seeing the sunset over the Aiguilles de Bavella, or the sheep on the mountain ridges, not to mention the unforgettable views of the sea - aren't these natural wonders worth the effort?