The British Airways i360 tower comprises a giant glass-and-steel doughnut that moves up and down a 162-metre-high pole, offering views of up to 42 kilometres in all directions.
It is acknowledged by Guinness World Records as the world's most slender tower, with a diameter of just 3.9 metres at its widest point. It is also promoted as the world's tallest moving observation tower.
Located on the seafront in Brighton, England, the tower officially opens to the public on 4 August 2016.
Ahead of opening day, drones were flown around the building to capture both photographs and film footage of the tower, offering a preview of some of the sights that visitors will be able to see.
"Built at the landward end of Brighton's historic West Pier, British Airways i360 is a modern day 'vertical pier' that gives a new perspective on the city," said Marks Barfield co-director David Marks.
"Just as the West Pier invited Victorian society to walk on water, so British Airways i360 invites visitors to walk on air."
Marks and his partner Julia Barfield were also the architects behind the London Eye, which inspired a number of similar projects worldwide, including the Singapore Flyer and China's Star of Nanchang.
The i360's 18-metre-wide pod – completed earlier this year – is 10 times bigger than the capsules of the London Eye and will hold up to 200 people at a time. It will rise to a height of 138 metres.
"The glass viewing pod will slowly rise up a slender steel tower to a height of 450 feet to provide passengers with stunning views of Brighton and Hove, and a beautiful panorama of the south coast and English Channel," said Marks.
The attraction also includes a visitor centre with a 400-seat restaurant, a gift shop, a children's play area, an exhibition gallery, and facilities for conferences and other events.
Marks Barfield Architects is based in southwest London. Other projects by the studio include an elevated walkway through the trees of Kew Gardens and a proposed research centre for the Amazon Jungle with a bulging bamboo observation tower and more than nine kilometres of treetop bridges.
The studio first drew up plans for the i360 in 2005, but the project stalled in 2008 as a result of the global financial crisis. It was revived in 2014 by the local council, majority-funded by a loan from the UK's debt management office.
"Today we would like to thank all those who have supported the project over the past 12 years," added Marks. "It has been a fantastic team effort."