Mounted to the wall was a panel of buttons, illustrated by stick men and symbols open to wild interpretation. It transpired that they controlled functions such as toilet seat heating, the water pressure level of the electronic bidet, and music to cover, er, embarrassing noises. I had just one question: Which one was for the flush?

Japan is now so notorious for its complicated "smart toilets" that earlier this year the Japan Sanitary Equipment Industry Association standardized the pictograms on such controls to prevent foreign visitors, in particular, being accidentally squirted in the face when groping for the flush.

So how did Japan become the world's most sophisticated innovator in lavatories? It's all down to one company: TOTO, which celebrates its 100th anniversary this year.

In 1903, Japanese inventor Kazuchika Okura made a journey to the West. Dazzled by the gleaming white ceramic toilet bowls of Europe, he returned home determined to modernize Japanese bathrooms, which still consisted of outdoors squat toilets with no sewerage system.

By 1914, he had produced the first Western-style flush toilet in Japan, and in 1917 he founded the Toyo Toki Company -- to be renamed TOTO in 1970. In the decades that followed, TOTO became a household name for quality toilets. But it wasn't until the end of the 20th century that the company really started to innovate.

In 1980, TOTO created the Washlet. It sold for 149,000 yen (that was roughly $660 in 1980). The idea was simple: to integrate functions of the European bidet -- a type of sink intended for the washing the buttocks -- into an electric toilet seat.

Customers could attach the Washlet to their existing toilets, or a TOTO unit. The company was already distributing in Japan a similar product produced by an American manufacturer, but the firm's plan was to refine it.

"We always say: 'This can be better,' and try to commercialize the idea," says Madoka Kitamura, the current TOTO president.

To improve the concept, engineers perfected the temperature of the water until it was pleasantly warm -- never too hot or cold. Next, they worked tirelessly to find the ideal angle at which water should spray from the wand that extends from the beneath the seat.

After asking 300 TOTO employees to test various positions for optimum comfort and cleanliness, they found what is now called the "golden angle."

It turns out, 43 degrees is just right.

The Washlet wasn't an overnight sensation, but it found a high-end clientele. By initially focusing on selling Washlets to golf courses, TOTO targeted businessmen who, before long, were hooked. Flush executives installed Washlets in their homes, and when traveling on business demanded accommodation with a TOTO.

"When you look at hotel brochures from that time ... there is a column showing whether or not the hotel has a Washlet," says Nariko Yamashita, a TOTO public relations representative. "Nowadays, it's a standard fixture in Japanese hotels."

By 1998, 10 million Washlets had been sold and, by 2000, TOTO toilets were becoming common in public places -- restaurants, shopping centers, schools. Shihohiko Takahashi, an urban designer and professor emeritus of Kanagawa University, explains that department stores and supermarkets used Washlets to entice shoppers.

"Customers, especially female customers, go to places with nice and comfortable toilets," he says.

You'll never encounter a nicer highway restroom than in Japan. In 2015, TOTO hit the 40 million Washlet sales mark, globally, helping to solidify Japan's cult toilet status. In the fiscal year ending in March 2017, TOTO made 33.8 billion yen ($311 million).

Today, you can find TOTO Washlets at the five-star Shangri-la hotel at the top of the Shard in London, aboard Boeing 777 business class bathrooms, and even in washrooms at the Louvre museum in Paris. In short, the Washlet has become the ultimate washroom status symbol.

Just as the vacuum cleaner became known as a Hoover and the hot tub a Jacuzzi, the "smart toilet" is now often simply referred to as a TOTO. Not that other brands haven't tried to muscle in. Rivals from Panasonic to Toshiba produce toilets with more controls than your average TV remote, with LIXIL emerging as the closest rival with 24% of the Japanese toilet market, according to industry researcher Japan Journal of Remodeling.

But only TOTO has the cult status to warrant its own toilet museum. Located in Kitakyushu, southern Japan, the TOTO Museum has been visited more than 180,000 times since opening two years ago, far exceeding its operators' expectations.

As you'd expect, some of the exhibits are slightly tongue-in-cheek, such as The Neo, a poop-powered toilet motorcycle, which TOTO used as a marketing device as it traveled Japan a few years ago to promote its green agenda.

Takahashi explains that TOTO has become so special to Japanese people -- to the point where they will travel to a museum that pays homage to it --- because it both addressed the nation's "shame culture" while also promoting Japan as a high-tech innovator.

"Japanese people could not (in the past) say the word 'toilet.' They were shy... there are (the awkward) issues of sound and smell regarding the toilet," he says. With the Washlet, "these problems are solved" as TOTO developed the "equipment to remove the smell" and cover the sound. Japan embraced the toilet.

The main goal of the museum is to give a potted history of toilets. There is, after all, no better way to make people appreciate modern plumbing than to confront them with an old wooden squat toilet. The museum also hammers home TOTO's technological accomplishments over the past century.

It's not all about fancy buttons. TOTO, for example, has developed a special coating that leaves each toilet bowl ultra smooth, preventing debris from sticking to its surface. Its rimless bowls give germs fewer places to hide.

After every flush, the Washlet sprays what TOTO calls ewater+ onto the bowl -- this regular water has been electrolyzed to give it a slightly acidic pH value that kills bacteria, preventing nasty "toilet ring" stains.

"It would be good if they didn't have to be cleaned at all. If the toilets didn't smell bad or it the sound they made would be quieter," says Kitamura, adding that all of those ideas are being pursued. In the late 1990s, TOTO embarked on a quest to make the world's most efficient flush.

"It used to take about 13 liters (for a single flush) when I joined (TOTO), but then it became six liters, and people thought it was impossible to go lower," says Shinichi Arita, a TOTO engineer.

In 2002, TOTO launched the Tornado Flush. Instead of water coming from above, it is released from the side of the bowl, causing it to swirl around the bowl naturally, meaning less water is required. During the following decade, engineers worked to reduce the amount of water the Tornado required. By 2012, a single flush was down to 3.8 liters.

"We didn't think that was possible at all when I joined. I believe it was a great turning point," says Arita.

This year, TOTO released its newest, shiniest toilet: the Neorest NX. With a price-tag of $6,000, it is thought to be the world's most expensive toilet (barring those encrusted with diamonds, or made from gold). For comparison, the standard Washlet goes for $2,500.

And while its price tag may seem absurd, the Neorest NX is already on back order. Hand-sculpted into a futuristic form and then fired in a kiln, this toilet is created like a work of art rather than a bathroom fixture. And from the Tornado Flush to the Washlet bidet, it incorporates every piece of technology TOTO has to offer.

When asked about the company's future, Kitamura says lower costs toilets are also in the works.

"There are many countries where toilets are yet to spread and sewage systems are yet to be developed. For those countries to develop, it's critical to save water and use less water," he says. "In India, for example, if one billion people use a 4-liter TOTO flush instead of 10 liter (flush), they can enjoy richer lives." 

TOTO is also eying foreign markets such as China, and branching out into high-tech bathing, having unveiled its cradle-shaped Flotation Tub at an industry fair in Germany earlier this year. Expected to go on sale in April, the circular tub is inspired by flotation therapy and promises to put users in a trance-like state.

But perhaps the biggest opportunity on TOTO's horizon is the Olympic Games coming to Tokyo in 2020, which will expose toilet-users from across the globe to its washroom wonders.

"We are planning to install the latest models to various places such as airports to increase people's chances of using a TOTO," says Kitamura. When it comes to the magic of a TOTO toilet, he explains, seeing is believing. Or perhaps that should be spraying.