We found Apple's mysterious office in Berlin (AAPL)

The discrete office is on the second floor of Markgrafenstraße 34, which overlooks the famous Gendarmenmarkt square in the centre of Berlin.

The office, which Apple has never publicly confirmed the existence of, was linked to the highly secretive Apple Car project last April and its location has been a mystery until now.

There are no Apple logos to be seen but the company does have its name next to a tiny buzzer outside the building's main door.

Apple did not respond to Business Insider's request for comment.

How we found the Apple office

It wasn't easy and it's taken several months of asking around.

Apple did not respond to us on several occasions and more than a dozen Berliners working in the city's tech industry said they had no idea that Apple had an office in the city when Business Insider asked them about it.

Eventually, a source in the Berlin startup scene told us that Apple has an office near — arguably Berlin's most magnificent square — but they declined to give us the exact address. They did, however, give us one more clue by saying it was close to Einstein Kaffee, which is a coffee shop on the corner of Gendarmenmarkt.

When we visited Einstein Kaffee on Tuesday, a barrista told us that the Apple office was next door on the second floor.

Apple's name and logo are missing from the second floor slot on the sign in the window but the company does have its name next to a little door buzzer that's easy to miss.

We asked a man leaving the building if Apple was indeed inside and he confirmed that the tech giant quietly moved in around a year ago. He said he wasn't sure how many people Apple had in the office because the elevators only take people to the floor that their key cards have access to.

We then called Apple's camera-equipped buzzer three times but got no answer.

As we stood outside, blinds were lowered over the windows of the Apple office, possibly to prevent us photographing any confidential company information that may have been visible on the walls inside.

What the office is used for

It's all a bit of a mystery but it's possible to make some educated guesses based on previous reports.

Last April, a report from German publication Frankfurter Allgemeine said "Apple is running a secret laboratory for the development of an automobile — and this in the middle of Berlin."

At the time, the report said the laboratory was reportedly home to 15-20 staff with backgrounds in engineering, software, hardware, and sales.

LinkedIn suggests that Apple has 168 people working in the "Berlin area." Many of these employees work in the Apple Store in Kurfürstendam but LinkedIn shows that Apple has dozens of engineers working in Berlin as well.

Mapping is one area where Apple seems to be focusing its engineering efforts in Berlin. The company has hired at least half a dozen employees from automotive mapping company Here — owned by Audi, BMW, and Daimler — for a Berlin-based Apple Maps team.

A source, who wished to remain anonymous, told Business Insider last April that Apple strategically moved in on Here's talent as the mapping company was passed from Nokia to the German automotive group.

"It's a simple story: Here was in disarray after Microsoft's acquisition of Nokia," said the source, who works in the Berlin tech scene. "Apple saw the opportunity and opened an office in Berlin, specifically to siphon Geo Information Systems (GIS) talent." The source said they did not know where the Apple office was when we asked them.

Apple's self-driving car efforts are known internally as "Project Titan." They have been the subject of rumours and speculation for years, and Apple's focus is now believed to be on building autonomous software rather than an entire vehicle.

There may be hundreds of of people working on the project. At one point, former Ford engineer Steve Zadesky, who helped build the iPhone, and Johann Jungwirth, who was Mercedes Benz's R&D chief, were both working for Apple.

Documents obtained by Business Insider earlier this month gave us a first look at this technology, which is "capable of sending electronic commands for steering, accelerating, and decelerating and may carry out portions of the dynamic driving task." Human drivers remain in the vehicle when the self-driving mode is engaged, and can override it at any time.

Apple CEO Tim Cook visited BMW's German headquarters in 2014, according to a Reuters report last January, which also stated that senior Apple executives went on a tour of BMW's Leipzig factory to learn how it manufactures the i3 electric car.

Silicon Valley heavyweights like Google and Uber are carrying out their own research into autonomous cars, as are many of the traditional car manufacturers, including BMW, Daimler, and Volkswagen.