“Bastia has a difficult relationship to the sea,” muses architect Dietmar Feichtinger. This medieval city, tucked away on the mountainous French Mediterranean island of Corsica, sits well above sea level, making up-close encounters with the water uncommon. Along the rugged northeastern coastline here, Feichtinger has recently completed Aldilonda, a 1,500-foot-long walkway hugging the craggy cliffside, between a 14th-century citadel and the waves below.