Some tourists look around them but Hidetoshi Ishii prefers to look down.

The 65-year-old is a manhole cover hunter. He has spent the past two decades touring with a folding bike and map, on the lookout for treasures.

“It’s like finding a gem. When I spot one, I can’t help smiling,” Ishii beamed.

A retired Tokyo Metropolitan Government official, Ishii was drawn to the world of manhole covers in his 40s, when his eye was caught by a particularly colorful design in Ise, Mie Prefecture. It depicted a group of people on a pilgrimage to Ise Shrine in the Edo Period (1603-1868).

“It was pretty,” Ishii recalls. “After seeing that, I thought it would be interesting to look for different designs across Japan.”

Since then, his hunt for manhole covers has become a driving force in his travels. A typical day sees him cycling long distances, sometimes more than 100 km.

Over the course of his travels he has clocked up 1,700 municipalities and 4,500 photos.

Ishii’s is among a growing legion of hobbyists enchanted by what he sees as the beauty manhole cover design. Enthusiasts are taking to social networking services such as Twitter and Instagram to share their joy, and the photos fly back and forth.

“They are works of art. The designs embody details and subtlety of the Japanese aesthetic,” said Hideto Yamada, a leader with Gesuido Koho Purattofomu (Sewerage Promotion Platform), a group of professionals and enthusiasts that includes officials from local governments and the infrastructure ministry’s sewage management department.

“Japan’s manhole covers are cultural properties we can be proud of,” Yamada said.

According to GKP, there are roughly 12,000 different manhole cover designs in Japan. Each depicts a local attraction or theme, such as Mount Fuji and the Yokohama Bay Bridge.

Municipalities began making decorative manhole covers in the 1980s after being told by a high-ranking official from the former infrastructure ministry that they could be used to promote and improve the image of Japan’s sewerage system, according to the Japan Ground Manhole Association.

Those behind the art are the manhole cover manufacturers themselves. They submit designs to a municipality, which then chooses a winner and commissions pieces.

As manhole cover designs usually embody something related to the area, fans say guessing the reasons behind the pictures is something of a game.

“Other countries also have beautiful manhole covers,” Yamada said. “But I believe none have designs that differ from one municipality to another.”

The growing legion of fans enjoy the thousands of different designs in different ways. While Ishii is among those who simply take photos, others get down and dirty to make ink impressions of the covers.

There are also those who hunt down rare antiquarian pieces from the prewar era rather than the typically colorful modern covers.

The growing fan base supports an increasing number of events that celebrate the manhole. These include the annual Manhole Summit, which began in 2014, and the so-called manhole night in Tokyo, where enthusiasts get together and share their knowledge, Ishii said.

In a bid to lure more people into the world of manhole covers, GKP in April launched collectible picture cards.

The cards can be obtained for free at municipal facilities such as local sewage plants.

GKP issued the first batch of 30 designs in April. They were so popular that the group reprinted an additional 30,000 cards the following month, Yamada said.

This month, 44 new cards were introduced.

Now in his mid-60s, Ishii admits he is no longer able to bicycle huge distances as he is not as strong as he once was.

But whenever he hears of a manhole cover design he has not seen before, especially one in Kanto, he cannot resist bagging a photo of it.

“I can’t contain my excitement,” Ishii said.

“In March I heard that (the Tokyo city of) Chofu made six different types of manhole covers sporting ‘GeGeGe no Kitaro’ anime characters. So I went, and it was thrilling to finally spot the last of the six designs.”