Illustration: Umihotaru (Tokyo Bay Aqua-Line).
The Tokyo Bay Aqua-Line consist of a 4.4 km long bridge and a 9.6 km long tunnel across the Tokyo Bay. It connects the cities Kawasaki and Kisarazu (opened 1997).
The man-made island Umihotaru (at the bridge-tunnel crossover) with an observation deck commands a 360-degree panoramic view of the Tokyo Bay.
Regarding the mountain in the far background, which appears from Umihotaru, which appears from Umihotaru, seems to be the Mt. Otozure-yama 186 m. There is no high mountain on the the Bōsō Peninsula in the Chiba Prefecture (highest point is the Mt Atago 408.2 m).
Many thanks to Kumiko Hamamichi (Japan) for the translation and identification of the mountains.