Tokyo Bay Aqua-line is a bridge and tunnel construction that extends across Tokyo Bay and links Kanagawa with Chiba. It opened in 1997 after over 23 years of planning and 9 years of construction and a cost of ¥1.4 trillion. Prior to this, traffic had to make the 100km semi-loop around Tokyo Bay to reach the southern half of Chiba’s Boso Penisula.
The construction is 15.1km long in total—9.5km of which is an undersea tunnel extending from the Kanagawa side. The road then raises above sea level at one of Japan’s most famous car park areas—an above-water rest area called Umi-Hotaru—before continuing for another 4.4km on a bridge until reaching Kisazaru in Chiba.
Umi-Hotaru (“Sea Firefly”) was given the name because it has the appearance of a ray of light coming out from the water. It is not your typical rest area. There are five floors of restaurants, shops, and cafes, as well as a viewing deck on the top from where you can look back onto Tokyo and see the Kaze no To twin towers which provide ventilation to the Tokyo Bay Aqua-line tunnel. See the website for more details of the facility.
The tunnel-bridge costs about ¥3,000 for cars, although this drops to a more reasonable ¥800 if you use ETC (in-vehicle electronic cards used for the toll gates in Japan).