Billion-dollar startup TransferWise has a sauna inside its office

TransferWise is a currency transfer startup that lets people send money around the world for far cheaper than it normally costs through bank transfers.

The company just raised a load of new funding. It brought in $58 million from investors including Andreessen Horowitz, which values the company close to $1 billion. And big-name American VC Ben Horowitz is going to join the company's board. TransferWise is all set for its international expansion.

But tucked away behind a door in TransferWise's head office in London is something rather unusual: A sauna.

The TransferWise sauna isn't just for display purposes. Employees say that they regularly make use of it.

There's a heater:

And also some birch twigs (which you hit yourself with, apparently):

Here's how you can tell how hot it is inside:

It makes sense that TransferWise has a sauna in its office: The company is Estonian. Co-founder Taavet Hinrikus was Skype's first employee (Skype is Estonian too), and TransferWise also has a large office in Estonia. So the sauna is a reminder of home for the company's Estonian founders.