Visitors walked up a spiral staircase in
the center rotunda of the Colosseum to see a 360 degree view of
London on the surrounding wall. Scaffolding is still up in 1829,
awaiting worker's completion.
Source: Ackerman,
Aquatint. The Interior of the Colosseum in Regent's Park, 1829 in
Barker F, Jackson P. London -- 2000 Years of a City & Its
People, 1974.