Astor Mansions rises 102m above Jeppe Street. It looks like it was designed by someone who could not make up his mind if he was building a modern skyscraper or a temple, or perhaps a rocket - even though in 1931 rockets were no more than the stuff of fevered imaginations.
Either way, all that matters is that Astor Mansions has not only survived, it has been protected from the ongoing predations of careless development and urban decay.
The same can't be said for Arop House, a few doors down. Arop House has been hijacked - one of many buildings in downtown Joburg to have suffered this fate - and is not, to put it politely, looking its best.Architect Brian McKechnie, who is taking us on an impromptu tour of the city's glorious (and not-so-glorious) Art Deco landmarks, is less polite about Arop House.
"It's a disaster," he says as we stand in front of the building and gaze at its shabby exterior.
Beyond the peeling paint and the trashed exterior and the broken windows, you can, of course, still see the things that once made it such a classic Art Deco delight - the relief panels, the sweeping vertical lines, the gorgeous curved brackets holding up the balcony and the flagpole - always a flagpole - on the roof.
"Art Deco loves flagpoles," says McKechnie.The contrast between the buildings is in many ways the story of our times. There on the corner, looking north, is Astor Mansions - high, proud, preserved. It represents not only a desire to protect South Africa's architectural heritage, but also a wish to revive downtown Joburg's fortunes as a place to live and work.
Arop House, however, is the perennial cautionary tale of the city's downtown blight, the reason Joburgers are afraid to come to town.Art Deco, which sought to bring clean, often streamlined shapes into design, emerged from the International Exhibition of Modern Decorative and Industrial Arts, held in Paris in 1925.
The six-month exhibition attracted 16 million people, who came to see art and jewellery, furniture, glass and other decorative arts brought to the fair by some 15,000 exhibitors.As beautiful as the jewellery and art is, it was in architecture that the movement realised its full potential. It was a reaction - and an antidote - to such influences as Cubism and the slightly fussy and pompous Art Nouveau eras that had preceded it.
Architects seized on the excitement of the age, when industry was vigorous and sexy (these days, industry may be vigorous, but few would call it sexy).
It was a time of beautiful ocean liners and streamlined steam locomotives hauling fast trains across the US and Europe. It was the dawning of the age of aviation - the short time when air travel would actually be glamorous.
It was the Jazz Age and a time of writers - literary superstars - like F Scott Fitzgerald and Gertrude Stein, Ernest Hemingway and William Faulkner. It was the best of The Great Gatsby in full cry.Buildings gave expression to the age in strong vertical lines that drew your eye upwards. There were streamlined shapes that reminded people of luxury ocean liners and the Zeppelin airships that then seemed like the future of air travel. There were acres of marble floors, brass lift doors and more brass strips lining windows and doorways.
Friezes depicted factories and ships and - closer to home - the dramatic shapes of mine headgear, the hoists that lifted the gold ore out of the earth.
Amid all the progress, there was an ongoing fascination and delight in the ancient world, seen in decorative motifs - such as the elevator doors in New York's exquisite Chrysler building - drawn from Ancient Egypt, and most dramatically in the ziggurat, or stepped pyramid, which underpins the shape of Art Deco structures such as Anstey's building in Joubert Street.Art Deco offered hope, modernity and freshness to people trying to forget the horrors of World War 1, and while the Great Depression in 1929 put the brakes on the movement, its influence continued to spread around the world.
New-minted South Africa, with gold and diamonds under its feet, was ready for it.
A PLACE IN THE SUN
Johannesburg in the 1920s was an up-and- coming city desperate to tap in to the global mood. Some people called it "Little New York". McKechnie smiles.
"I think that's quite generous," he says.
Still, the city has one of the largest concentrations of Art Deco architecture on Earth. That it may (or may not) be in third place behind New York and Miami is not important, but that we even think in such terms is a reminder of how the city came to have so much Art Deco.
"The city had that South African obsession with anything not South African," says McKechnie. "People were obsessed with modernisation and mechanisation and here you had this city which had been born in gold and was being built for the third time."As he speaks, we are standing in Commissioner Street - the city's heart of Art Deco buildings.
Nearby are London House and Howard House - both built as small, speculative offices for lawyers and doctors. After a bit of a scramble, we get permission to take pictures in the Howard House lobby - its brass lift doors, with their heavily stylised "H", are one of the loveliest sights of the tour.
Now, from where we stand on Commissioner Street, we can just see the fine Old Mutual and SA Permanent buildings.
This was once the heart of the city's insurance district, and the large firms that set up here wanted to make a statement. Before us is the Security Building (the view of it ruined by the eyesore of a BRT bus stop right in front) with its beautiful friezes, including a dramatic lighthouse.
Looking east, we gaze up at the considerable bulk of His Majesty's, site of the eponymous theatre that stood between its two office towers - in one of which Advocate Joe Slovo once had chambers.
The two steel crowns that topped the towers are long gone but that does little to detract from the building's own majesty. Nearby, Shakespeare House is undergoing a thorough renovation and the builders watch us lugubriously as we pick out its details.We are quick learners and I am gripped by the clues at every building we stop at, looking for the brass work or the friezes or the little flourishes that say "Art Deco".
We spend three hours walking the streets and looking at buildings. At no point does it feel unsafe. Downtown Joburg is busy and vibrant - taxis, hawkers, shoppers and builders jostle for space.
Even outside Arop House, which looks like the centrepiece of a post-apocalypse movie, people are busy going about their day. Still, it would be unwise to walk here alone with a camera slung around your neck.We amble up Rissik Street, past the burnt-out ruin of the Post Office and its ravaged clock tower, to the Barbican. This was Joburg's first skyscraper, designed by architects Obel and Obel - a name that crops up often here - and was briefly its tallest until they were ordered to ensure that Astor Mansions, being built a few blocks away, was even higher.UPS AND DOWNS
McKechnie shepherds us down Jeppe Street, past Astor Mansions, to two of the jewels in Johannesburg's Art Deco crown - Manners Mansions and Anstey's building, the latter finished two years ahead of Manners, in 1937.
Both were designed as department stores with apartments on the higher floors. Tenants at Manners once included the French Model School and Henry Gluckman, Jan Smuts's health and housing minister. Anstey's was famous for its tea room and the beautiful brass monkeys in its lobby.TAKE A WALKING TOUR
Past Experiences offers walking tours of Joburg's attractions, ranging from the street art of the city to shopping in the CBD to exploring the spices and tastes of Fordsburg. All tours are on foot or by public transport such as the Rea Vaya rapid transit bus. Guides are all graduates and have the necessary tourism qualifications and will show you a different side to this incredible city. 
Alternatively, along with tours that examine the legacies of mining and of architect Sir Herbert Baker, the Johannesburg Heritage Foundation also offers a dedicated tour to all of Joburg's Art Deco landmarks. You can join any of the tours listed on the calendar or book a private tour...