At the nearest marked reference point at the foot of Marischal Street is the location of the now vanished Regent Bridge. This connected the warehouses on the north side of the harbour and the city centre to the Blaikies Quay area.
Note on Regent Quay several very ornate granite buildings with their lavish stonework decoration nestled beside old fashioned Mews - or alleyways that led through to narrow side on buildings in back streets (known in Scotland as a "close") where there were densely packed tenement housing often with several families to a single small dwelling. A typical Victorian contrast of lavish displays of wealth next to extreme poverty.
The area looked very different back in Victorian times when the Regent Bridge existed. Instead of where there now is a fence was a wide open area that went all the way to the quayside edge next to the water. The area was covered with several brick built warehouses. These no longer survive and have been replaced by a modern warehouse shed with the whole area fenced off from the public.
At the marked reference point outside the Maritime Museum you can view an original stone marker that was removed when the bridge was demolished. I'd encourage you to visit the museum it has many other interesting facts about the harbours history and the cities link to its maritime past and future.
Grateful thanks to University of Aberdeen for permission to use the archive photos.