One column contains a spiral staircase leading to a parapeted walkway along the entablature. This staircase was closed to the public in 1926 after a 15-year-old boy fell to his death from the top of the monument. The structure fell into disrepair in the 1930s and was fenced off, then repaired in 1939. It has since undergone further restoration, including extensive work in 1979 during which its western side was dismantled. Floodlit at night since 1988, it is often illuminated in different colours to mark special occasions. The National Trust began to offer supervised tours of the walkway in 2011.