Blackfriars (aka Black Fryers) Stairs down to the Thames are at the end of Water Street on the South-central edge of this segment of the 1746 map. http://www.motco.com/map/81002/SeriesSearchPlat...
The overlays that highlight 17th century London features are approximate and derived from:
Open location in Google Maps: 51.511256, -0.103780
Chart showing the number of references in each month of the diary’s entries.