What is the big circle thing in London?

The London Eye is a giant Ferris wheel on the South Bank of the River Thames in London. It is the most popular paid tourist attraction in the United Kingdom, and the most popular Ferris wheel in Europe. The Eye is 135 metres (443 feet) tall and has a diameter of 120 metres (394 feet), making it the fourth tallest Ferris wheel in the world. It is also the tallest fully cantilevered Ferris wheel in the world, meaning that it is not supported by any guy-wires. The Eye has 32 capsules, each of which can hold up to 25 people. A full revolution of the wheel takes about 30 minutes. The London Eye offers stunning views of the city, including the Houses of Parliament, Big Ben, Westminster Abbey, and Buckingham Palace.