A general view shows the "Myaku-Myaku", the mascot of the 2025 Osaka Expo as the Gundam pavilion is seen behind on the first day of the six-month 2025 Osaka Expo in the city of Osaka on April 13, 2025. Philip Fong, AFP 

A multi-eyed mascot, a vast wooden Grand Ring, 160 countries and regions strutting their stuff, and robots and sushi galore: Expo 2025 began on Sunday in Osaka, Japan.

World Expo is held every five years in different global locations. Here are five things to know about this event, which runs until mid-October.

- Grand Ring -

Encircling dozens of national pavilions is the Grand Ring -- recognised by Guinness World Records as the planet's largest wooden architectural structure.

Architect Sou Fujimoto says his edifice, which cost 34.4 billion yen ($230 million) and has a circumference of two kilometres (1.2 miles), is a symbol of unity.

Latticed beams hold up a sloping roof, 20 metres (65 feet) tall at its highest point, which doubles as a "skywalk".

Fujimoto told AFP that he chose wood as a sustainable material.

But Japanese media say just 12.5 percent of the temporary structure will be reused -- down from the original plan of 25 percent.

- 'Mysterious' mascot -

Myaku-Myaku, Expo 2025's mascot, is red and blue with five googly eyes dotted around its smiling mouth -- and one more eye on its bobbly red tail.

It is "a mysterious creature born from the fusion of cells and water", according to event organisers.

"Basking in the sunlight is the source of its energy" and sometimes the shape-shifting Myaku-Myaku "forgets its original form", they say.

Despite puzzled reactions when it was unveiled, the mascot has since become popular among social media users in Japan, and has even inspired fan art.

- Slow sales -

This is Osaka's second World Expo after the 1970 edition that was attended by 64 million people, a record until Shanghai in 2010.

At Expo 1970, the first film in IMAX format was shown and visitors admired rocks brought back from the Moon.

But this time ticket sales have been slow and many locals are unimpressed by the construction being 27 percent over budget.

Organisers want to sell 23 million tickets overall, and as of last week, 8.7 million had been sold. To encourage visitors, same-day admission will now be possible.

- Meteorites and Marley -

Japan's pavilion has a meteorite from Mars discovered in Antarctica by Japanese researchers -- the first time it will be on display to the public.

Hungry visitors can stop by Japan's longest sushi conveyor belt before checking out cutting-edge robots, drone shows and a beating "heart" grown from stem cells.

The US pavilion, themed "America the Beautiful", has an LED-screen simulator of a NASA rocket launch.

Elsewhere visitors can help polish five heart-shaped "Love and Peace" rocks, while the Jamaica pavilion features life-size Bob Marley and Usain Bolt statues and a bobsleigh.

- Ukraine 'peace' -

Russia announced in 2023 -- the year after it invaded Ukraine -- that it would not participate in the Expo.

But Ukraine is present, despite its dire financial situation caused by the war -- a decision that Osaka's governor has said "conveys peace".

It will reportedly show 18 objects including helmets used in the restoration of power facilities damaged by the Russian invasion.