‘Up at the O2’

Visitors to London can ascend a walkway over the roof of the O2 (Peninsula Square, London; phone +44 161 385 3211), formerly called the Millennium Dome. (The shell was completely redesigned; only the roof was kept.)

The climbing surface is made of a tensile fabric and leads to a platform 52 meters (170 feet) above the ground at the top of the structure, with views of the Thames Barrier, Olympic Park and Canary Wharf.

The 380-meter (1,246-foot) guided tour takes 1½ to two hours and is recommended for those who are physically and medically fit. Walkers must be at least 1.2m (four feet) tall, not weigh more than 286 pounds, and must be able to walk up an incline of 28 degrees and down one of 30 degrees. Climbers will be attached to the walkway system but may move around freely on top.

Book tickets in advance. £22 ($35) each. All climbing and safety gear is provided.