How Sydney Builds a $6B City on 150,000 Tons of Poison

Added: 2026-05-13

[00:00:00]150,000 metric tons of toxic black tar sat buried under Sydney for a century.

[00:00:07]This $6 billion project, Bangaroo South, forced engineers to fight the ocean while digging up a poison graveyard.

[00:00:15]They built a giant city that breathed through a secret basement. How do you keep a twisting skyscraper from falling in the wind? Long ago, the Kadagal people fished in these clear blue waters and hunted on the shore. But in 1841, the land changed forever. Workers built the first gas works ever seen outside of Europe right here. They burned coal to make gas for street lights so the city would be safe at night. This helped Sydney grow, but it left a deadly mess behind.

[00:00:50]For 80 years, the ground soaked up black colar and dangerous chemicals. In 1921, the plant finally closed down. The government buried the poison under thick concrete and turned the area into a port for shipping containers.

[00:01:08]Everyone forgot about the toxic sludge hidden beneath the surface. In 2009, the plan for Barangaroo South began to take shape.

[00:01:17]Engineers knew they could not just build on top of the old tar. They had to dig it all out and clean the land. This was the start of a 15-year war between modern machines and a century of pollution. But how did they clean up a city of poison without making everyone in Sydney sick? Engineers found that they had to move 150,000 metric tons of dirty soil. If they just started digging, the toxic smell would have covered the whole city. To stop this, they built giant tents over the areas where they were working. These were huge buildings made of steel and strong fabric. The tents were kept under negative pressure, which means air could only go in and not out. They used giant fans to suck all the air through special carbon filters to catch the smells and dust inside. Workers had to wear special suits and masks to breathe safely while they dug up the black tar. They removed 10,000 cubic meters of the most dangerous material from deep inside the rock. Because the site is right next to the water, the holes they dug would fill up with the ocean. This water became dirty as soon as it touched the soil.

[00:02:35]The team built a special water treatment plant on the site. This plant cleaned over 140 million L of contaminated water. They made the water so clean that it was safe to pump back into the harbor. This part of the project alone cost over $125 million.

[00:02:55]It took over 5 years to make the land healthy again. If cleaning the ground was hard, what happened when they tried to build a basement inside the ocean?

[00:03:05]The engineers had to build a giant basement that is 77,000 square m in size. This is like a hidden city under the towers. To build it, they had to keep the harbor water out. They built a thick wall made of concrete and steel all the way around the site. This is called a diaphragm wall. To make it, they used big machines with special claws to dig deep, thin trenches into the ground. As they dug, they filled the trench with a heavy mud called bentonite.

[00:03:38]This mud was thick and pushed against the sides of the trench so they would not fall in. Then they put in giant cages made of steel and poured concrete from the bottom up. The concrete pushed the mud out. When the concrete got hard, it became a solid wall that water could not go through. The rock underneath is sandstone, but it is not flat. It goes down deep as it gets closer to the water. In some places, the rock is 18 m down, and in others, it is 33 m down.

[00:04:13]This meant some parts of the wall had to be much deeper than others. For the tallest tower, they used a way to build called top- down construction. They pushed giant steel poles called plunge columns deep into the ground. This let them build the tower going up while they were also digging out the basement underneath at the same time. This saved a lot of time, but it was very noisy and dark for the workers in the hole. The basement had to be perfectly waterproof.

[00:04:44]They used special monitors to check if the walls were moving even 1 mm.

[00:04:49]The walls have to hold back the weight of the whole ocean every single day. But what kind of massive machine stays hidden in this dark basement to keep thousands of people cool? The basement holds a giant machine called the district cooling plant. This machine is so big it can cool all the buildings in the whole neighborhood. It has 10 large units and two small ones that work together.

[00:05:16]Usually every big building has its own air conditioner on the roof, but those machines use a lot of water and make a lot of noise. Instead, the engineers use the harbor to stay cool. This is called a harbor water heat rejection system.

[00:05:32]Every day, the plant sucks in water from Sydney Harbor. The water goes through screens and filters to make sure no fish or tiny animals get hurt.

[00:05:43]This cold harbor water passes through pipes to take the heat away from the buildings. The harbor water never touches the water inside the buildings.

[00:05:52]It just takes the heat and carries it back to the ocean. When the water goes back, it is about 7° warmer than before.

[00:06:00]This system is great because it saves 100 million L of fresh drinking water every year. It also keeps the roofs of the towers clear so people can build gardens or put up solar panels. The plant can create 62 megawatts of cooling power. It uses special pipes that are 400 mm wide to carry the cold water. The basement does not just cool the buildings. It also creates its own water. But how can a neighborhood make more water than it actually uses?

[00:06:33]Bangaroo South has a special water recycling factory in the basement. This is part of the plan to be water positive. This means they want to make more clean water than they take from the city. The plant can make 1 million L of recycled water every single day. It takes all the dirty water from toilets, sinks, and showers in the towers. Then it uses a process called sewer mining to take even more dirty water from the city's main pipes. The plant uses tiny living things called bacteria to eat the waste in the water. Then it pushes the water through very fine filters. These filters are so small that not even a germ can get through them. The result is very clean water that is safe to use for flushing toilets and watering all the plants in the parks. This saves over 200 million L of water every year. By doing this, the neighborhood helps the whole city of Sydney save water when it does not rain. With the ground ready and the basement working, the engineers look toward the sky to build the tallest tower in the city. But how do you stop a giant twisting tower from falling over?

[00:07:48]The Crown Sydney Tower is the tallest building in the city at 271.3 m. It has 75 floors and a very special shape. The architects wanted it to look like three flower petals twisting together as they grow toward the sun.

[00:08:06]Because of this twist, the building moves 60° from the bottom to the top.

[00:08:12]This made it very hard to build. The columns that hold the building up are not straight. They are called helical columns because they follow the curve of the twist. Some of these columns lean at an angle of 4°.

[00:08:26]Every floor in the tower is a different shape. This meant the engineers had to use computer models to figure out where every piece of steel and glass should go. They also had a problem called axial shortening. This happens when the weight of the building makes the concrete floors below get a little bit shorter.

[00:08:46]Because the building is so tall, this can add up to a big change. The engineers had to plan for this so the windows would still fit. They used special tools to measure the building every single week. They even put sensors inside the concrete to see how it was moving. At one point the building reached level 43 and actually started to move in a different direction. This happened because they stopped pouring concrete for 20 days. They had to use some of the biggest cranes in the world to lift the heavy parts. One crane could lift 100 metric tons in one go. Another crane was very fast and could lift 25 metric tons to the top in just 1 minute.

[00:09:31]These cranes worked even when the wind was blowing at 72 kmh.

[00:09:37]Crown is not the only giant on the shore. Right next to it sit three glass crystals that look like they are floating in the air called one Sydney harbor. The tallest one is 247 m high.

[00:09:51]These towers were designed by Renzo Piano who is a very famous architect. He wanted them to be very clear so they would reflect the water and the sky. To do this, they used 18,000 glass panels.

[00:10:05]10,000 of these panels are on the first tower alone. This glass is very special because it lets in light but stops the sun from making the rooms too hot. This helps the people inside use less energy.

[00:10:20]The buildings also have special fins on the outside that move to block the sun.

[00:10:25]These towers were built with over 31,000 cub m of concrete. They used electric machines instead of diesel ones to build the third tower. This helped stop pollution while they were working.

[00:10:38]Factoring in the energy and carbon costs, the electric machines were over 50% cheaper to run. This project cost $850 million just for the building part.

[00:10:51]Since it started, people have spent over $4 billion to buy the apartments inside.

[00:10:57]One apartment at the top sold for $141 million.

[00:11:02]This is a record for the most expensive home in Australia. Steel and glass are the normal way to build. But what happens when you decide to build a skyscraper out of nothing but wood?

[00:11:14]Bangaroo South has two buildings that are made of engineered timber. They are called International House and Damu House. They are six floors high and are the first of their kind in Australia.

[00:11:26]The engineers used a type of wood called cross- laminated timber or CLT.

[00:11:33]This is made by gluing layers of wood together in different directions to make them very strong. They also used glue lamb which are big beams made of wood.

[00:11:43]International House used 950 cub m of glue lamb and over 2,000 cub m of CLT.

[00:11:51]These buildings are much better for the earth and concrete ones. The wood stores carbon instead of releasing it. Damu house was built very fast. It only took 7 months and 16 people to finish the main part. This is much faster than a normal building which usually takes 60 people. They used wood that was grown in forests in Austria. Even some of the columns were made from old wood that was 80 years old. This wood was salvaged from old telegraph poles and warehouses.

[00:12:24]These buildings show that we can build big things without hurting the planet.

[00:12:29]Towers and parks need people to fill them. But how do you move 40,000 people every hour through a tunnel hidden under the ocean floor? To get all the workers and visitors to Bangaroo, the government built a new metro station. This station is part of a big project to build 30 km of new train lines under the city. The station is deep underground and has an entrance on Hixon Road. To build the station box, engineers used 6,500 metric tons of steel. They also used 11,000 cub m of concrete just for the walls. The concourse level, where people walk, was made using 98 massive concrete beams.

[00:13:15]Some of these beams are 15 m long. The station can handle over 14,000 passengers every single day. In February 2026, the station was already very busy.

[00:13:27]4,500 people were using it in just 1 hour in the morning. The station is so scenic that it won a gold award for its design in early 2026.

[00:13:39]It has gardens and art that tell people who lived there first. The trains stop at a station that leads to a secret cavern hidden under a hill. But how do you turn a giant concrete cave into a worldclass party spot? The cutaway is a massive underground space at the northern end of Bangaroo.

[00:14:00]It was carved out of solid sandstone rock. For a long time, it was just a big empty room, but in 2026, it has been transformed. The project cost $100 million.

[00:14:14]Engineers installed 13 giant wooden trees that are 13 m tall inside the space. These trees look beautiful and help support the ceiling. They also fix the acoustics, so the sound is perfect for concerts. The cutaway is very green and uses renewable energy for everything. It can hold 3,000 people for festivals and art shows. It officially opened for 24/7 events in May 2026.

[00:14:43]People can now walk through a huge tunnel to see the old sandstone walls while enjoying music and art. This space is connected directly to the new metro station by a secret walkway. This makes it easy for thousands of people to visit without needing a car. The whole project is now a major part of the city, but it has not been without its troubles in 2026.

[00:15:08]The total cost of Bangaroo South was over $6 billion and it supports $23,000 jobs in the city. It has become a famous landmark that people from all over the world come to see. The project generates $1.5 billion for the economy every year.

[00:15:26]It shows how a dirty, poisoned dock can be turned into a place where thousands of people live and work every day. If you want to see more of the world's biggest and most difficult engineering projects, make sure to like this video and subscribe to the Ultimate Mega Builds channel. We would love to hear your thoughts on these twisting towers and the giant machines hidden in the basement. So, please leave a comment below and turn on your notifications so you never miss another story about the world's greatest builds.