Umihotaru (海ほたる / Umi-hotaru) — the rest-area / artificial island on Tokyo Bay along the Tokyo Bay Aqua Line at Nakazima, Kisarazu, Chiba prefecture, Japan, was officially opened on December 18, 1997. The name Umihotaru (海ほたる, “sea firefly”) is inspired by the glow of bioluminescent sea creatures like Vargula hilgendspots.
It’s an artificial island/rest stop built in the middle of Tokyo Bay at the point where the underwater tunnel portion of the Aqua Line transitions to a bridge.. The structure is multi-story (5 Floor), combining parking and facilities, and surrounded by 360° views over Tokyo Bay.
★The Beautiful 4th floor observation deck
★The Cutter Face, the ultimate tunnel cutter blade
★The Cool breeze
★The observation desk from 4th Floor
★The Tokyo Bay
★The Escalator
Umihotaru serves as a unique highway parking and rest area (parking, shops, restaurants, observatories) while also acting as the junction between the tunnel and bridge sections of the Tokyo Bay Aqua Line.
It is often said to be the world’s only highway rest stop built over the sea, the only rest area on a toll expressway that sits in open water.
★From the parking view
★From the Parking
There were 15 of us, just visiting this highway parking lot, seeing the ocean, seeing the ‘cutter face’ used to build the tunnel. ocean breeze, tropical vibe, so much water all around, and if you’re lucky, you can even see Mount Fuji.
History
Before the Aqua-Line, traffic between Tokyo / Kawasaki (Kanagawa Prefecture) and the Bōsō Peninsula (Chiba Prefecture) had to go all the way around Tokyo Bay — either via Tokyo and Chiba’s northern route or by ferry. This detour was about 100 km, and highways were heavily congested. The Aqua-Line cut the distance dramatically now only about 30 km across the bay.
★the view of Tokyo Bay
★Observation Desk
★with my Husband
In the 1980s and 90s, Japan was in a period of large-scale infrastructure projects showcasing technological power. Building a undersea tunnel and bridge across Tokyo Bay was a world-class engineering challenge. The project demonstrated Japan’s leadership in tunnel boring, marine construction, and seismic engineering. By directly linking Kanagawa, Tokyo, and Chiba, the Aqua-Line aimed to stimulate economic growth, attract industry, and encourage tourism in Chiba prefecture.
Construction & the Tokyo Bay Aqua Line
Tokyo Bay Aqua Line, (東京湾アクアライン, Tōkyō-wan Aqua Line) is a combined tunnel-bridge expressway that links Kawasaki (in Kanagawa Prefecture) to Kisarazu (in Chiba Prefecture) across Tokyo Bay. It consists of a 9.6 km submerged tunnel from the Kawasaki side, which emerges at Umihotaru, then continues via a 4.4 km bridge portion toward Chiba. The total length of the Aqua Line is about 23.7 km including all access sections.
★Aqua Line, the Tunnel under the Tokyo Bay
Construction Monument – Cutter Face
Construction Monument: Cutter Face (建設記念碑・カッターフェイス- Kensetsu kinenhi kattāfeisu) refers to the enormous shield machine cutter head used to bore the underwater tunnel portion of the Tokyo Bay Aqua-Line. After construction was completed, part of this massive machine was placed on display at Umihotaru as a monument to the project.
★Cutter Face, the ultimate tunnel cutter blade
★the view of Tokyo Bay
★obersavation Desk
★Cutter Face
- A cutter face is the rotating front part of a tunnel boring machine (TBM), also called a shield machine.
- It consists of a giant steel disk (often 10–15 meters in diameter for large tunnels), fitted with multiple cutting bits that grind through soil and rock as the machine advances.
- Behind the cutter face, the TBM supports the tunnel wall with precast segments, making excavation safer in underwater or soft-soil conditions.
★Tropical coast vibe
★The view of Cutter Face
★The Blade of the Cutter face
★ The cutter face, history shared
The Tokyo Bay Aqua-Line tunnel runs 9.6 km under the seabed from Kawasaki toward Umihotaru. For this, one of the largest TBMs in the world at the time was built — with a cutter face around 14 meters in diameter. This enormous machine excavated the underwater section while withstanding water pressure, soft ground, and seismic risks.
The cutter face represents the pioneering spirit of Japanese engineering in the 1990s. It is a reminder of the difficulty and ambition of building a 10 km tunnel under Tokyo Bay — in 90’s, at the time, one of the most challenging tunnel projects in the world.
★The Ship alike deck
★The 5th Floor Deck
★The Umihotaro view
The Monument at Umihotaro
After completion, part of the TBM’s cutter face was preserved and installed at Umihotaru as a construction memorial. A tribute to the engineers and workers who built the Aqua-Line. An educational display, showing visitors the scale of the machinery required for such an unprecedented tunnel project.
- The cutter face monument is located on the observation deck area, easily visible to travelers, and has become one of Umihotaru’s iconic photo spots.
★The Glass architecture
★Drone is strictly prohibited
★All floor Guide
Observation Decks & Views
The top floor include observation decks where you can enjoy panoramic views of Tokyo Bay, the surrounding skyline (Tokyo, Yokohama, Chiba), and even glimpses of the bridge and sea.
★Interior of a Ship
★Tokyo Bay
★The highway road of Umihotaro
Shops, Restaurants & Facilities
Umihotaru has multiple floors: the lower ones are parking, and the upper floors are devoted to shops, restaurants, cafés, and amusement facilities. You can find Japanese fare (ramen, soba, sushi, tempura), Western-style food, cafés like Starbucks, desserts, souvenir shops, and local goods. The Umihotaro have the ancient artifacts open for all.
★ The Umihotaro on a Bird eye
★The Ocean Going Ship Umihotaro
★The different types of Tied rope
★The parking exit
★3rd Floor view
Cost, Opening, & Toll:
Toll: The tolls are substantial: for standard cars, the cash toll is about ¥3,140, but with ETC (electronic toll payment) it’s cheaper (¥2,320). On weekends & holidays, ETC users pay a further reduced toll (~¥1,000) for standard vehicles.
Wheelchair Accessibility: 
Yes
Wheelchair accessible restroom: yes
★Wheelchair accessible restroom, diapar chaing sation
Opening/Closing Time: 24/7 Open
Paking: A Generous paeking, wheelchair accessible Parking: yes
★Parking space of Truck and Normal vehicles
★Electronic vehicles charging station
EV Charging: yes
Your detailed coverage of Umihotaru, from its history to accessibility features, is really inspiring. Keep sharing such valuable insights 
What a fascinating read,