A groundbreaking project is taking shape in , Saudi Arabia, one so massive that it could fit 20 inside. Dubbed "The Mukaab," this colossal cube-shaped structure is set to become the by volume, dwarfing any other existing megastructure.

The Mukaab is the centrepiece of Saudi Arabia's ambitious New Murabba development, a futuristic downtown district aimed at transforming the capital city into a global hub for tourism and commerce. The cube itself will stand 400 metres tall, 400 metres wide, and 400 metres long, making it a "supertall skyscraper" in height while also being five times larger than the Boeing Everett Factory, the current record holder for the world's largest building by volume.

Construction for the building is expected to cost $508 billion (£400 billion).

Inside, plans call for an immersive, high-tech environment where visitors will step into a world of digital illusion.

A giant holographic dome will be installed at its core, capable of transporting guests into hyper-realistic virtual landscapes, from deep-sea adventures to futuristic cities and even Mars.

At the heart, the Mukaab will be a spiralling tower filled with luxury hotels, restaurants, cinemas, and entertainment venues, a structure larger than the Eiffel Tower.

Surrounding it will be additional towers and 350,000 square meters of underground space, providing room for retail, residences, and leisure attractions. The rooftop, rather than being left unused, is planned to feature a massive garden.

This ambitious project is part of Saudi Arabia's Vision 2030, a nationwide strategy to reduce the country's reliance on oil and diversify into tourism, technology, and entertainment.

The Mukaab is expected to be completed in time for the 2030 World Expo, which Saudi Arabia will host, potentially making it the centrepiece of the international event.

Michael Dyke, CEO of the New Murabba Development Company, described the project as "the most complex engineering thing ever undertaken." Initial scepticism surrounded the announcement in early 2023, with many dismissing it as an impractical concept.

However, by the end of 2024, construction was already underway.