When you're a billionaire founder of one of the world's biggest companies, buying a massive yacht to sail around the world would surely be one of the first things you'd do.

And of all the ports in the world you could sail to, surely sunny Singapore is worth a visit.

Mothership reader Daryl Tan spotted Paul Allen's yacht docked in Keppel Marina on his way to Vivo, at about 11am on Oct. 9. He snapped two photos of the enormous sea-going vessel, which you can see below:

The yacht's name, Octopus, can be seen on the side, and the words Octopus George Town can be seen on the bow. According to Tan, there was a guard stationed near the yacht, who watched him while he was taking the photos.

According to Forbes magazine, the Octopus is one of the top 10 most expensive yachts in the world, costing US$200 million to build and with an annual operating budget of at least US$20 million. It's 126m long, and officially classed as a "megayacht".

This floating city is equipped with a recording studio, full-size basketball court, seven smaller boats, enough room for a 60-strong crew, two helipads, and two of its own submarines that can explore the ocean floor and serve as a mini-hotel for guests to sleep in.

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Allen is known to rent out his yacht for private use, including exploration projects, scientific research initiatives, and rescue missions, so he might not be on that yacht right now.

In Aug. 2017, the yacht was responsible for the discovery of the wreck of the USS Indianapolis, the US Navy heavy cruiser that was sunk by a Japanese submarine in the Philippine Sea during World War 2.

Still, it takes someone with serious cash to be able to rent one of the world's most expensive yachts from the co-founder of Microsoft. Perhaps we'll read about another of its discoveries soon.

Top image from Daryl Tan.