Penguins “fly across the sky” in a new water tank that officially opened on July 12 at the Sunshine Aquarium in Tokyo’s Toshima Ward. (Takayuki Kakuno)

When visitors enter the Sunshine Aquarium in Tokyo’s Ikebukuro district from July 12, they won’t believe their eyes at the latest feature--and with good reason, as the “flying penguins” are a clever optical illusion.

The display appears to show penguins flying through the sky, thanks to a strategically placed rooftop water tank that perfectly shows through a view of high-rise buildings and blue sky.

The front pane of the tank hangs overhead from aquarium visitors, like an awning made of water.

When penguins swim in the tank, it looks as if they are flying between skyscrapers and above the spectators’ heads.

According to the aquarium, it has clinched a world-first in displaying the flightless birds in such a setting.

“Having conversations with visitors, I sometimes notice some don’t even know that penguins are avian,” said aquarium keeper Mutsumi Ueda, 36.

“They cannot fly, but please come to see them swimming as if they were flying over the urban sky.”