Completed in 1998, Akashi Kaikyō, west of central Kōbe, can still claim the title of world's longest suspension bridge (based on its main span, which measures 1991m). Take the lift up to the Maikō Marine Promenade, a 320m walkway 47m above sea level over the bridge's northern end (try not to freak out over the glass floors!). From here there are beautiful views over the Inland Sea.
The JR Kōbe line runs from Sannomiya to Maikō Station (¥300, 20 minutes), from where it's a short walk to the visitor centre (follow the signs and the promenades running over the main road).
The bridge connects Japan's main island, Honshū, with Awaji-shima, which is then connected by another bridge to the island of Shikoku.