Ancient mysterious ruined cities

Nice Australian piece giving snapshots of what they call "Ancient ruined cities that remain a mystery." Not sure I agree that Pompeii "remains a mystery" but they have some fun choices here. My favorites:

Derinkuyu, Turkey
The largest and deepest of 200 underground cities in the Cappadocia region, this eerie location was home to approximately 20,000 people (plus livestock, a church, school and kitchen). The inhabitants dug tunnels and rooms beneath their homes in the soft volcanic rock.
The city reportedly grew to 85 metres and 11 levels deep. It is believed to date back to the early Byzantine Empire, as early as the 7th-8th centuries.
People fled to the area to find safety from anti-Christian Romans, bandits, and later on, anti-Christian Muslims. Huge rocks were rolled across the entrances, with air shafts letting fresh air in. It was sealed up at some point after the 10th century but reopened in 1969.

This one I had not heard of. Sounds like a fascinating way of life. I'm wondering if this was referenced in Assassin's Creed: Revelations.part of which took place in an underground Christian city in Cappadocia.

Machu Picchu, Peru
It's the destination at the top of many travellers' bucket lists. The spectacular 'lost city' of Machu Picchu in Cusco was discovered in 1911 and is one of the most famous sites created by the Inca Empire.
In a remarkable feat of 15th-century construction, the Incas flattened the top of the 2430 metre high mountain to accommodate 140 structures including temples and houses. The city was divided into areas for royalty and the lower classes.
And it's not the jawdropping architecture that's the most puzzling part of Machu Picchu. How they ran a vast empire in an isolated area of Peru without building any marketplaces is quite puzzling, and dramatically different to most other old cities, where market squares were key. Why did they have no recognisable economy, and how did they prosper without it?

Machu Picchu has been called "The Lost City of the Incas," but actually it is not. The term "Lost City of the Incas" is actually a reference to Vilcabamba, which was actually the last capital and refuge of the Incas and was destroyed by the Spanish. The location of Vilcabamba had been lost for almost 400 years. For a while Machu Picchu was thought to be Vilcabamba, but Machu Picchu was intact, had not been touched by the Spanish, and may not have even been a town at all, but some sort of religious center. Works starting in the 1970s going up to 2000 have definitively identified the site of Vilcabamba as a site deep in the Ecuadoran forest known as Espíritu Pampa, which from a development standpoint was a steep drop from the Inca heyday in Cuzco.

Great Zimbabwe
The giant, walled and wealthy city of Great Zimbabwe was home to around 30,000 people at its peak in 1200-1450. An important trade centre, it was rich in gold from local mines. The technologically advanced city features a huge enclosing wall some 20 metres high and was believed to have served as a royal palace for the Zimbabwean monarch. Famines may have contributed to its mysterious demise.

Great Zimbabwe is a rather curious case. It's peak may have been 1200-1450, but technologically the town looks more like Bronze Age Mycenae or Troy. No one knows why Great Zimbabwe fell, though as suggested above speculation has focused on famine. Even more curious, no one knows what the purpose was of the Great Conical Tower of Great Zimbabwe. It's completely solid, with no entrance.

A tower with no entrance: the Great Conical Tower of Great Zimbabwe.

As I said above, I probably would not have put Pompeii on this list, since we know so much about its demise. Hisarlik, the site generally but not universally believed to be the mythical city of Troy/Ilion, fits much better, because we still don't know why, how or at whose hands Troy ended. For that matter, we don't know that about Mycenae or pretty much any other place in Bronze Age Greece.

But perhaps the most mysterious city that deserves to be on this list is Mohenjo-daro, in the Indus River Valley of Pakistan. Of all the ancient civilizations whose ruins have been identified, Mohenjo-daro may be the one about whom the least is known. I'll let Exploring Dystopia take it from here as to some of the creepy details:

In ancient history, advanced civilisations evolved around rivers: Egypt around the Nile river and Mesopotamia around the Eufrat and Tigris rivers. Less well known is the mysterious civilisation which evolved around the Indus river in India, 2500-1500 B.C.
In the old religious texts called Rig-Veda, it is told how the war god Indra — also known as Puramdara, the "castle destroyer" — destroyed ninety fortifications. These castles probably belonged to Dasyas, a people briefly mentioned in the Rig-Veda and described as strangely dark. No ruins were ever found, though, and for many years the Indus civilisation was considered to be a mere myth.
It was not until 1921-22 any remains of this lost civilisation were to be found: the ruins of two cities called Harappa and Mohenjo-daro (the latter means "The Heights of Death"). Unfortunately, building material from the cities had been used by British colonists to build railway embankments, especially in the case of Harappa.
The cities are located in hostile environments, salt desserts with the worst climate in India. The climate was probably more suitable when the cities were built, but it seems conceivable the environment has been at least partly destroyed by merciless exploitation.
Harappa and Mohenjo-daro are twin cities, literally; they have almost identical structures. They are both examples of remarkable city planning. Large boulevards stretches through the cities along a north-south axis and all street and alley crossings have right angels, just like in fairly modern cities.
Judging from the ruins, all appartment buildings were standardised with two floors, small rooms and a courtyard in the center. The building material is baked mudbrick of the same size and weight, which indicates governmental control of weights and measures. Doors and windows always face the courtyards and alleys, never the streets. Thus, the streets of Harappa and Mohenjo-daro were surrounded by plain brick walls. There are almost no decorations, which is remarkable as later Indian architecture is famous for its rich detail.
There are many indications of a strong central government. This is most obvious in Mohenjo-daro, which is better preserved than Harappa. The city plan is dominated by a building complex called the Citadel, which is located on an artificial, 15 meter high hill. The Citadel was most probably the financial and governmental center of Mohenjo-daro and possibly the cult center as well. The largest building is undoubtedly a granary, but it is not known for sure what the functions of the other buildings were. There are indications that the city had a kind of police force, but no military buildings such as castles have been found. Mohenjo-daro also has an advanced sewer system, more advanced than many sewer systems in the Third world today. Hygiene seems to have been important, as there are large baths in both cities and basins in every building.
The Indus writing is yet to be deciphered. Many examples of their writing have been found — on seal stones, pot shards and walls — but they are seldom longer than half a dozen letters. There are few examples of art as well. One of the best preserved stone sculptures depicts a man with well-groomed beard, narrow eyes and a subtle smile, described as a tyrannical sneer. Two anatomically perfect torsos have also been found, so well crafted that many archaeologists doubt their Indus origin. Compared to ancient Egypt and Mesopotamia, there are extremely few cultural findings.
Why the Indus culture ended is uncertain. There are three possible explanations:

• Natural catastrophes such as flooding.

• Thoughtless exploitation such as over-use of the soil.

• Conflicts such as invasions or civil wars.

Very few corpses have actually been found in the ruins and in all cases the cause of death seem to be summary executions. Judging from this, the Indus culture might have ended because of an invasion.
Everyone who have been exploring the cities of Harappa and Mohenjo-daro have found them monotonous and depressing. The cities are strictly utilitarian in their design and there are few, if any, expressions of beauty. Walking through Harappa and Mohenjo-daro has been described as walking through the ruins of some modern mining city like Lancashire. The buildings have been compared to Soviet barracks and the Indus culture has sometimes been called "1984 B.C."! There is undoubtedly something cold and anonymous over the Indus culture.

That statue of the "man with well-groomed beard, narrow eyes and a subtle smile, described as a tyrannical sneer" is this:

Count Dooku? Saruman? The "Priest King" of Mohenjo-daro bears an uncanny resemblance to Christopher Lee.

The statue is generally known as the "Priest King," presumably because he bears an eerie resemblance to Christopher Lee. In reality, no one knows what the statue represents or what it was for.

Which is pretty much par for the course for the Indus River Valley civilization of which Mohenjo-daro was a part. Aside from the ruins, we know almost nothing about it. And unless we can find a sort of Rosetta Stone that allows us to decipher its language, we may never know much more about Mohenjo-daro.