The site matters more than the building. This is where the first Fort William stood, the one Siraj-ud-Daulah took in June 1756, and the guardroom that became known as the Black Hole was somewhere under the present steps.
Walter Granville, who also designed the Indian Museum and the High Court, put up the GPO in 1868 with a tall Corinthian colonnade and a dome faced in lead. The rotunda inside is one of the better interior spaces in the city and is still a working post office.
Brass strips set into the pavement on the north-east side mark the outline of the Black Hole cell as it was surveyed in the nineteenth century. Most people walk over them without noticing.
The Postal Museum upstairs holds early Indian stamps, including the Scinde Dawk of 1852, the first adhesive postage stamp used in Asia. It keeps irregular hours.
What the guidebook leaves out
The brass lines in the pavement. They mark the Black Hole outline, and there is no sign explaining them.
