Umihotaru

Halfway across Tokyo Bay, the Aqua-Line highway does something extraordinary: it stops being a bridge and plunges into a tunnel under the sea. At exactly that transition floats Umihotaru (“Sea Firefly”), a five-story rest stop on an artificial island in the middle of the water.

Why It’s Interesting

It is the most spectacular highway service area in Japan — a ship-shaped building surrounded by open sea, with viewing decks that look back toward Kawasaki and Tokyo on one side and out across the bay (and, on clear days, Mt. Fuji) on the other. Inside are shops and restaurants; outside sits the giant rotary cutter head that bored the undersea tunnel. Standing on a sunset deck, cars vanishing into the sea beside you, is pure modern-Japan spectacle.

Best Time to Visit

Year-round, but go for sunset or after dark, when the bay and the distant city skylines light up.

Getting There

There’s no train: you reach Umihotaru by driving the Aqua-Line (it links Kawasaki and Kisarazu) or by highway bus. It’s a perfect first or last stop on a Boso road trip.