The General Post Office (GPO) is one of the great pieces of colonial-era civic architecture on the Mall — a long Indo-Saracenic facade in red sandstone with a central clock tower, completed in 1887 to mark Queen Victoria's golden jubilee. The lobby is still in regular use and worth stepping into; the original mahogany counters and ironwork have largely survived.
The GPO marks the point where the Mall changes character — from the museum and Charing Cross at the colonial end, to the busier commercial stretch heading east. Worth pausing for, particularly if walking the colonial-era route.