OSAKA (Kyodo) -- A giant circular timber roof known as the "Grand Ring" that is to be the centerpiece of the 2025 World Exposition in Osaka was illuminated for the first time Thursday in a test run.

The massive structure, with a circumference of approximately 2 kilometers and a maximum height of around 20 meters, appeared to float in the evening darkness on Yumeshima, an artificial island in Osaka Bay.

The ring will serve as the main promenade for the expo site, allowing visitors to walk along the rooftop for uninterrupted 360-degree views or underneath it, where they will be sheltered from rain and sunlight during the event, which will run from April 13 to Oct. 13 next year.

The ring features approximately 5,000 lighting installations that will illuminate differently to reflect seasonal changes.

"I recommend visiting at dusk when the sky changes colors," contributing lighting designer Hiroyasu Shoji said.

Part of the ring extends over the water in the bay, allowing visitors a close-up view of the planned water performances during the event.

The ring's structure was completed in August, with the remaining installations, including the addition of greenery, expected to be finished by February, the Japan Association for the 2025 World Exposition said.