Awaji is surrounded by Akashi Strait and Naruto Strait and connected to Honshu island by Akashi Kaikyo Bridge which is the world's longest suspension bridge.
Awaji Island is the largest island in the Seto Inland Sea and located in southern Hyogo. Facing the Osaka Bay on the east and the Harima-nada on the west, the island is surrounded by the Akashi Strait on the north and the Naruto Strait south to west and its coastal area is a part of Seto-naikai National Park.
On Mt. Mikuma in Sumoto City, the site of the Sumoto Castle built early in the 16th century, where some stone walls and the keep that forms the castle's center remain. The castle tower commands a full view of the city and the Osaka Bay. Awaji Island also boasts places worth a visit to enjoy the natural scenery, like Uzushio in which the tide as fast as about 10 knots rises in all sizes of whirlpools, and many beaches including the Goshiki-hama Beach known for colorful pebbles made by the erosion of waves.
Akashi Kaikyo Bridge is the world's longest suspension bridge, 3,911 meters long overall with two cable-braced main towers spaced 1,991 meters apart. This bridge, which links Awaji Island with Kobe, is nightly illuminated in seven different colors to regale the eyes of viewers.
From Tokyo :
[Rail] About 3hrs to Shin-Kobe Station from Tokyo Station by JR Tokaido Shinkansen Line. About 2hrs from Shin-Kobe Station to Sumoto Bus Centor by JR expressway bus.