Elon Musk also appears to be building a mysterious glass structure in Austin. Known as Project 42, the 'secret' plans have been described within the company as a house for Musk. Renderings of the building show different styles of glass structure: one a twisted hexagon perched on the waterfront, and another a large glass cube, similar to the Fifth Avenue Apple Store in New York, pictured here.

Tesla employees were said to have been working on the development before the project's financing came under scrutiny by the US government. An order for millions of dollars worth of specialised glass sparked an internal investigation by Tesla lawyers. While the outcome is unknown, Manhattan federal prosecutors launched a probe into whether the company's funds were misused, The Washington Post reported.

Inside the incredible homes of the world's wealthiest billionaires