Try to find the spot where the photographer was standing.
Looking south towards what we would now call Railway Square, towards the point where George Street became George Street West (and later Broadway). The horse buses would shortly be replaced by steam and then electric trams as Sydney's first railway terminus became Sydney Central Station. Enlarging the picture reveals a steam tram at what was then called "Railway Gates" at the corner of Deveonshire Street and today's Lee Street.
Yikes! It's rush hour!
That is some turnout right there! I can imagine the sight, sound & smell of the horses clip-clopping, all the horse $&#! & the murmurings of massed crowds... ;0) On a side note, no safety helmets, no seat belts, climbing over rooftops and carriages, no barriers or barricades for public safety - we think we have come so far as modern society - but regarding personal freedoms - have we really? :0)
The twin turrets (see note) are the only building surviving - GoogleMapsStreetView - www.google.com.au/maps/@-33.8831435,151.2037868,3a,75y,22...
The crowds might suggest the opening of the new Sydney Station in 1906 before the construction of the Marcus Clarke department store over the shops to the right in 1909.
"The present station was officially opened on 4 August 1906 and opening for passengers on 5 August 1906. The new station included the previous Mortuary railway station used to transport funeral parties to Rookwood Cemetery. The last train departed platform 5 of the 1874 station at midnight. During the remainder of that night, the passenger concourse was demolished and the line extended through the old station into the new station. The Western Mail arrived at 05:50 on 5 August 1906 at the new station. Devonshire Street, which separated the two stations, became a pedestrian underpass to allow people to cross the railway line and is now known by many as the Devonshire Street Tunnel."
The Marcus Clark department store was later built in 1909 over the shops to the right so it was long before any Boxing Day Sale crowd queues.
[https://www.flickr.com/photos/highranger] You are right; something HUGE was going on! Great story, but I think this is before late 1899, otherwise the George Street tramway poles and wires would be in full view. See this later (1901-1906) photo from Mr Macpherson, and the slightly different fashions - [https://www.flickr.com/photos/statelibraryofnsw/37038276805/]
ps I think Mr Macpherson is on top of a horse-drawn omnibus!
I think this one is at the same time - [https://www.flickr.com/photos/statelibraryofnsw/36658571050/in/dateposted/]
Public holiday crowds most likely. Pre 1899 as tramway electrical span poles not present.