Hiroko walks down the street with her eyes fixed firmly on the pavement. What does her friend's town have to offer in the way of manhole covers? There is one with a picture of a fish, one showing Mount FujiAn active volcano in Japan. It is considered a sacred mountain. , one with flowers, and - yes! - even one with a Pokemon figure. She must put it on Instagram!

Hiroko is one of the thousands of people in Japan known as "manholers". Such is their enthusiasm that they travel far and wide across the country to photograph manhole covers or take rubbings of them with paper and charcoal.

They collect replica covers and themed ephemeraCollectable items that were once expected to only be useful only for a short time. - from keyrings to trading cards, which can fetch high prices at auction. They even meet for "manhole nights" to discuss their hobby, and attend exhibitions and lectures about it.

One leading manholer, Hidetoshi Ishii, has cycled to over 1,700 towns and cities to indulge his passion. He has exhibited his photos at the Tokyo Sewage Museum and written a book called Manholes of Japan: What Manholes Have Taught Me. He is also the founder of the Japan Manhole Research Association.

The idea for ornate designs emerged in the 1980s. Japan's sewer system needed expensive modernisation, and a clever civil servant saw the covers as a way of winning popular support for the project.

Today 95% of Japan's municipalitiesA town or district that has a local government. have their own special designs. They feature local landmarks, traditions and tourist attractions. The Tama district of Tokyo specialises in Hello Kitty covers, reflecting the theme of a local amusement park.   

The announcement last week that the city of KyotoKyoto, once the capital of Japan, is a city on the island of Honshu. The Kyoto Protocol was an international treaty which extended the 1992 United Nations Framework Convention on Climate Change that commits state parties to reduce greenhouse gas emissions. is to sell off vintage covers for £30 each has caused great excitement. Demand is expected to be so high that buyers will be chosen by lottery.

"Little satisfies or showcases the human capacity for ambition, vision, love and connoisseurshipExpertise in a particular subject, such as a type of art. as much as a good collection," writes Leo Lewis in the Financial Times. Among the world's great collectors have been Nancy Hoffman (umbrella covers), Myk Briggs (ear trumpets) and Nick Vermeulen (airline sick bags).

The documentary-maker Jonathan Gili collected everything from pencil sharpeners to sardine tins. When he died in 2006, his hoard was valued at £100,000.

The craze for manhole covers has yet to catch on in other countries, though a few years ago the London artist Maria Vlotides created a "pavement poetry" trail in Notting Hill. It consists of coalhole covers with inscriptions by local writers such as Sebastian Faulks and Margaret Drabble.  

The idea that even the most basic object can be made to look interesting has much to be said for it. In a current series for BBC Radio 4,¹ the designer Thomas Heatherwick argues that boring cityscapes damage people's mental health.

But one journalist, Rupert Wingfield-Hayes, sees decorated manhole covers as symptomatic of Japan's decline. "They are works of art," he admits.² "But each one costs up to $900 (£741). It's a clue to how Japan has ended up with the world's largest mountain of public debt."

Yes: The value of an object is dictated purely by the demand for it. In the 17th Century, people in the Netherlands paid extraordinary amounts of money for tulip bulbs in an episode known as "tulip fever".

No: You cannot put a price on the things that matter most in life - love and friendship. Even a banknote is valueless in itself: it is a simply a piece of paper whose worth we choose to believe in.

Or... The Irish writer Oscar Wilde was right to define a cynic in his play Lady Windermere's Fan as "A man who knows the price of everything, and the value of nothing".