A section of timber roof at Tokyo's Olympic Gymnastics Centre was raised in the Japanese capital, marking the halfway point in the temporary venue's construction.
The 10,000 seater arena will host gymnastics during the Olympics and boccia during the Paralympics in under two years' time, with the roof raised in 200-tonne sections.
It is hoped that the entire structure will be in place by May next year, with construction currently said to be on time.
However, those in charge of the project say they are still anxious about meeting the deadline.
"The construction work is progressing very speedily," the director of venue development Toshihiro Hosokawa told Channel News Asia.
"Next year, at the end of October, the Centre will be completed so there is only a year to go, hence my mixed feelings."
The venue, which is located in the Ariake district of Tokyo, will be used as an exhibition centre after the Games, although it has been designed to be dismantled by 2030.
Partly to make it easier to deconstruct, and partly to showcase Japan's timber industry, the 90-metre roof has been made from local larch.
The head architect Hidemichi Takahashi was quoted as saying sustainability was at the heart of the design.
"The design has a view on post-usage after the Games," he said.
"No major changes are needed for it to be used after the Games.
"From an eco-friendly point of view, this venue uses the most amount of wood out of all the Tokyo 2020 venues."