Lost Villas of Sydney: Woollahra, Orielton

Original
Today (Google)
The pics above and below are from about 1880. The estate on Ocean Street began in 1840, and by the 1860s this new, large house had been built.
Original
Restored
Subdivision in 1918 got rid of most the grounds but the house lasted until 1928, when it was demolished for flats. Plans about that are shown next...

Lost Villas of Sydney: Potts Point, Tor Cottage/Chatsworth

Original
Today (Google)
This is Tor Cottage in 1859, as seen from Grantham, looking up the Harbour to the Heads. It was built in 1849 as a single-storey, then extended up another level, not long before this photo. In the 1880s, it was sold and the new owner rebuilt it as a grand villa, renamed Chatsworth.

Lost Villas of Sydney: Potts Point, Prestonville/Cairo

Original
Today (Google)
This pic is from 1950. Originally built as a villa called “Prestonville” in 1876, it became the Cairo Hotel from 1911, until demolition in 1959 for the now-also-demolished Chevron Hotel.

Lost Villas of Sydney: Potts Point, Springfield House

Original
Today (Google)
This pic is about 1920. Originally built in 1830, like most early colonial villas it later had a grander makeover by richer owners. And like most of Potts Point's estates, by the 1940s it had been demolished for flats and shops.

Lost Villas of Sydney: Potts Point, Grantham


Original
Today (Google)
Rebuilt in 1870, Grantham estate ran from Macleay Street down to the water at Woolloomooloo, which is where the stone was quarried for it. Sold in 1917, it was progressively subdivided until ultimate demolition in 1937. This photo is from the 1880s.

Some more pics outlining its history follow the jump -

Bond St 1900

Looking west from Hamilton Street, which no longer exists as it was built over in the 1960s and 70s.
Original

Today (Google)

Macquarie Street 1857c

Original unrestored photo
Original
Today Google Maps street view location
Today (Google)

Standing on the upper verandah of the Mint building, looking north-west to what is today Martin Place. This one photo turned out to be the most epic, meticulous investigative work I've done so far.

The original image is so degraded, faded and lacking in detail that there is basically little more than some blurry shapes. It didn't even have a description, I had to work that part out. And yet, after cross-referencing decades of related maps, land registries and plans, and photos, I landed at an extremely satisfying outcome. This is most likely the earliest photo that exists of Macquarie Street, historically the most important Australian governmental street at the time.

All of the following information about the image is from my own research.

The Sydney Cyclorama. 1898 Railway Square

Opened in 1889, it was the 19th-century equivalent of an IMAX theatre - a massive, purpose-built immersive environment. The structure dominated the Railway Square area.
The Cyclorama as it appears in the background of an Ultimo photo.
Original 1898
In the original image, it's way up the back on the right. There aren’t any photos where the actual building is the subject, I think because it had no street aspect. Located on a battle-axe block surrounded by other properties, it only presented a doorway entrance squeezed between other buildings on George Street.
For its entire 18-year run, it showed just one exhibit: The Battle of Gettysburg. This was a massive 360-degree painted canvas, a copy of another famous US cyclorama. To heighten the "being there" effect, the visual spectacle was accompanied by active light and sound, - explosions, bugle calls, and the flashes of cannons. They even employed a war veteran to pace the platform and give first-hand reminiscences of battlefields to the crowds. To bridge the gap between the audience and the 2D painting, a 3D diorama filled the foreground. Real dirt, stonework, timber fences, shattered wagon wheels, and mannequins were arranged to blend into the painted horizon. 
From an unrelated artist's impression of Railway Square in the 1890s, we can see the Cyclorama's actual arrangement.

Today (Google)
If you’re interested in how it worked, I’ve collated some detailed info which explains the structure.

Circular Quay East 1900, 1870, 1884

Original
Today (Google)
The Quay, looking north from Phillip Street in 1900. The problem with poor quality original images, which is my favourite source - the poorer they are, the more satisfying the restoration - is the lack of fine detail. So while I was able to cross-reference the signs on the buildings from other contemporaneous photos, I was unable to put a name to the ship moored at the Eastern Australian Royal Mail Line wharf. Perhaps someone can assist?
Original 1870
Restored
Here is a wonderful 1870 view, looking back to Phillip Street at the direction of the 1900 image above. It shows how simple was the Quay in earlier Victorian times. Beginning in the 1840's, it was being developed from an ordinary V-shaped bay with mud flats into the circular walled wharf we have today, using literally decades of infill.

(As an aside, in quite a few photos taken in the early 1870s, there's a singular young chap stationed like a prop, similar to the one in the foreground above. It's such a regular feature that I wonder if it's the photographer's son. There were few people taking photos at that time, so it might be a sort of signature.)
Original 1884
Restored
Here is much the same aspect just fourteen years later. More buildings, more activity, but also there are grand buildings beginning to appear on the skyline. At top left is the Colonial Secretary's building, and top right is the Lands Department. We have transitioned from quiet outpost to wealthy colony.

As another aside, you may notice the very tall lightposts in the 1884 image (and 1900)? They were the brand-new technology arc-lamps; electric flood-lighting for night cargo handling. The port was so busy that night illumination was brought in to cope. Arc-lamps were primitive by our standards, as they spat loudly, gave off noxious fumes, and needed replacing every 75 hours. But they were incredibly bright, and also were a popular novelty for the locals. They lasted until WW1 when they were replaced with more cost-efficient electricity.

The Wentworth Hotel 1920 Lang Street

The Wentworth was one of the better hotels at the time, in the same league as The Australia, Metropole, Grosvenor, Petty's, and The Sydney.

"Will James' Band, Wentworth Hotel, Sydney, 1920. L to R: - violin (unnamed) ; Frank Bull - Piano ; Will James - banjo, leader ; Sid Simpson - saxophone ; Sammy Cope - drums"
I had a great time getting this photo of the band orchestra just right. In 1920, jazz was evolving from rag, and judging by the instrument line-up here the repertoire would have been very Dixieland. Unfortunately, recording studios didn't reach Australia until five years after this, so we'll never get to hear them. Although, you can get a good approximation from US recordings around 1919-1920 available on SoundCloud and Bandcamp.
Also, the female singers' outfits show the incredible change that occurred between pre and post WW1 society. That's skimpy compared to the long skirts that women had always worn. 
The Wentworth moved to Chifley Square in 1966, and the old site was cleared to make way for the new QANTAS building (currently IBM).
1938

Today (Google)

The Rocks 1901 Gloucester Street

Original Archival

Today (Google)
North from Essex Street. This is one of a comprehensive government survey series of photos of The Rocks taken in 1901, just before the mass slum clearance and rebuilding. I cropped this photo into the one at top as I thought the little chap with his baby sibling in its pram is really adorable, but also it's a familial insight into daily life at the time. He's looking up the street toward two women, perhaps one is their mum, standing near the Black Dog Hotel. The buildings beyond there on the right still exist, but much of everything forward has since been demolished, with the Cahill Expressway cutting through the middle.

Pitt Street 1871 Haymarket

Sydney Haymarket Gas Holders and Workmen in mid-Victorian era
These huge gas holders were in the middle of the city, between Central Station and the shopping area uptown, until 1922. They were opposite Belmore Park, across the road from the later Capitol Theatre, and supplied the southern part of the city with gas piped in from the AGL refinery at Darling Harbour, which was near today's Barangaroo. 
The sandstone building in the Google Street View below is a remnant of the Australian Gas Light offices built later in the Victorian period. When it was restored a few decades ago, the original signage was removed, but you can still make out some of the ghost lettering on the parapet.
Original

Today (Google)

Hyde Park 1932 and 1945

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Restored
This was the new Federation-style bandstand built in 1912 to replace an earlier Victorian one. It was in the centre of what is today's Sandringham Gardens. Having survived the massive excavations of the park when the subway was put through in the 1920s, it didn't survive WW2 because...
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... in 1945, the south-east corner of Hyde Park North, at the corner of College Street, was resumed to build a large repatriation hostel for British soldiers returning from the Pacific War. It was demolished in 1947 and replaced with new gardens, dedicated to our late Queen Elizabeth, that are still there today.
(For newer generations who may not have heard of it: The British Tucker Box was under a donation scheme of food parcels from the people of Commonwealth countries back to Britain, which was suffering shortages after the war.)

Phillip Street 1880s from Bent Street

Original

Today (Google)
A wonderful picture showing humble old Sydney with remnant original Georgian slab huts. The street was realigned in the 1960s to make Chifley Square. The church spire at the end on the left is St Stephen's which was demolished in the 1930s to make Martin Place. The spire on the right is St James.