AKASHI, Hyogo Prefecture--A restaurant toilet stall that allows hundreds of eyes to peer inside continues to elicit astonished reactions from its female users, much to the delight of the owner.

The “aquarium toilet” at the HiPoPo PaPa restaurant here is surrounded by glass walls of an illuminated tank filled with possibly peeping tropical fish. The toilet user essentially becomes immersed in a scene from a seabed.

“Sometimes, a customer comes out of the place and throws her arms above and sideways to explain to her companion how it looks like and all,” said Koichi Miyanaga, the 71-year-old owner of the restaurant. “It’s such fun to see my customers almost dancing.”

The restaurant in this western city offers a wide view of the Harimanada Sea, dotted with islands including Awajishima, Shodoshima and the Ieshima islets. But the aquarium toilet, which is a bit larger than a standard booth and has a slightly higher ceiling, is what has really wowed customers for decades.

The toilet is available only for female patrons because Miyanaga believes that women are “cleaner users.”

‘IMPOSSIBLE’ PROJECT

A fourth-generation heir to a building materials business, Miyanaga opened a predecessor to HiPoPo PaPa in 1980 in Akashi, where he grew up.

One day while swimming off Shodoshima island, he relieved himself in the sea, which gave him a “pleasant sense of openness.”

On another occasion, he saw a school of tuna swimming in a donut-shaped tank at the Tokyo Sea Life Park. He said he thought that “putting a toilet in the middle of that circle would be fun.”

The two experiences gave him the idea for the aquarium toilet.

However, design firms dismissed the toilet proposal for his restaurant as “impossible.”

Undeterred, he enlisted the help of his friends, including a carpenter and a glassworker, to build the toilet on his own.

Miyanaga insisted on using a glass fish tank instead of an acrylic one, which would have been vulnerable to scratches and other blemishes.

After a glass tank cracked under the pressure of about 16 tons of water, he built a stainless steel frame and used double panes of 18-millimeter-thick tempered glass. He fixed them with a type of plywood used in shipping containers to increase the strength.

Miyanaga also applied glass-fiber imitation rock to cover the unappealing sight of naked plywood exposed in the water.

The work was completed in a month and a half and after three blunders.

The project set him back 30 million yen ($284,000), but the work was done while Japan was in the middle of the high-flying period of asset-inflated economic growth in the late 1980s.

“Everything used to go at the time,” Miyanaga said, laughing.

Spread by word of mouth, the toilet became known around Japan.

“It really felt like I was in the middle of the sea,” said Naoko Mizuguchi, a 64-year-old resident of faraway Kawagoe, Saitama Prefecture, recently. “Although it was a restroom, it didn’t quite feel like one. That experience felt so good.”

DAILY MAINTENANCE

Only paying customers can use the aquarium toilet at the restaurant, which can be crowded with more than 1,000 diners a day after the nearby beach officially opens.

Male customers sometimes bring their girlfriends to the restaurant without telling them about the toilet so that they will be taken aback at the sight.

Male patrons can view the restroom in the company of a woman.

Maintenance is not easy nor cheap.

The faucet almost always remains open to keep the water at the right temperature of 28 degrees. Miyanaga’s monthly water bill is about 200,000 yen.

He also spends one hour every morning cleaning the tank and its filtering device.

The tank contains around 300 tropical fish, which have bred naturally. Miyanaga, however, appears quite indifferent to the creatures.

“I don’t know anything about what they are called and what species they are,” he said.

But he ensures the fish behave to prevent his customers from becoming spooked. He said he once “fired” a fish that had a grim look.

“The fish could intimidate a woman and discourage her from lowering her underpants,” he said he thought at the time.

HiPoPo PaPa is located at 57-1 in the Matsue district of Akashi. It is open from 10 a.m. through 6 p.m., although the hours can change. The restaurant has no scheduled closing dates.