Umi-hotaru is a nickname of a rest area on the
Tokyo Bay Aqua-Line, an expressway.
It means "sea firefly".
Tokyo Bay Aqua-Line is the expressway connecting between Kawasaki city
in Kanagawa Prefecture and Kisarazu city in Chiba Prefecture, and it is
built across Tokyo Bay.
The length is 14.0 km. The the west side (Kawasaki side) is 9.6 km undersea tunnel, and the east side (Kisarazu side) is 4.4 km bridge.
And there is "Umi-hotaru" rest area at the bridge-tunnel crossover point.
It is one of the rest areas, and has restaurants, shops and amusement
But the location is on an artificial island in Tokyo bay, then it has good views.
Many route bus from Tokyo, Haneda airport, Kawasaki and Yokohama to some cities in south part of Chiba Prefecture run this expressway and stop here.