Tower of Wind

When a strange structure with sail-like towers appeared in the middle of Tokyo Bay, the internet began to ponder its purpose. Some suspected—jokingly, one would hope—nefarious ends. Was it a secret government installation, or a supervillain’s underwater lair? Or maybe an early warning system for an encounter with Godzilla?

The truth was far more prosaic. It was, in fact, the Kaze no Tō, or Tower of Wind, a ventilation shaft supplying air to the tunnel section of the Tokyo Bay Aqua-Line.

Opened in 1997, the Tokyo Bay Aqua-Line is a bridge-tunnel combination that crosses Tokyo Bay. It consists of two bridges at either end, connected by a six-mile-long tunnel underneath the bay. The tunnel currently ranks as the fourth-longest underwater tunnel in the world, and the longest undersea tunnel for cars (the three longer tunnels all carry trains).

The Tower of Wind sits above the midpoint of the tunnel, which lies about 131 feet below the surface. Designed by the acclaimed Pritzker Prize-winning Japanese architect Toyo Ito, the two elegant towers look like domes from some angles and wind-filled sails from others. Each tower captures the almost constant winds that blow across the bay, supplying the tunnel below with fresh air.

Users of the Tokyo Bay Aqua-Line can stop at a second artificial island, known as the Umihotaru, located at the bridge-tunnel crossover point, which has a rest area with restaurants, shops and amusement facilities. The Tower of Wind, however, is off limits. But you can still see it from across the bay, or from the window of your plane as you fly into Tokyo's Haneda Airport.