By Steve Rosenberg
BBC News, Berlin
It is fight night in a smoky Berlin nightclub.
In Chess Boxing you have to either checkmate or knock out your rival
The lights go down, the stage door opens and out walks a pharmaceuticals salesman from San Francisco. David "Double D" Depto has travelled 5,000 miles (8,045km) in search of glory.
As he shuffles, then skips towards the ring, bare-chested and beating the air, this American muscle machine looks cool and confident. Seeing his opponent though, I would not be.
In the blue corner, solid as the Brandenburg Gate, stands a German riot policeman who goes by the name of "Anti-Terror Frank". And predictably the crowd is on his side.
A bell sounds. Seconds out - round one!
Rocky with rooks
But just when you would expect the punches to start flying, something rather odd happens.
The two challengers put on headphones, sit down at a table and start playing chess: in the middle of the boxing ring.
That is because this is Chess Boxing. A sort of Rocky... with rooks.
The rules are simple. There is one round of chess - and then one round of boxing. Punching power alternating with brainpower.
If you are wondering how they can move the pieces with their boxing gloves on, well, they take them off before the rounds of chess!
All in all, you have 11 rounds in which to either checkmate your opponent - or knock them out.
Berlin is hosting the first ever chess boxing world championship. It has been organised by the man who invented the sport - Dutch artist Iepe Rubingh.
David "Double D" Depto says the sport proves fighters are also brainy
"Chess and boxing have lots of things in common," Mr Rubingh assures me.
"If you move the pawn, it's like moving your jab. If you come with the knight, it's like a hook. If you come with the rook, it's a straight right. And if you march in with the queen, it's a knockout," he says.
Two sports in one means double the pain - and double the pressure.
In the run-up to the big fight, Anti-Terror Frank spent hours at his local Berlin gym to tone his mind - as well as his muscles.
"In Chess Boxing, 90% is in the head. Before you lose a fight, you give it up in your mind. So it's very important to have the physical, but also the mind strength to do this sport," Frank says.
But why do it in the first place? Why put yourself through all this physical and mental torture?
Chess Boxing is now being taught in one Berlin school
For David "Double D" Depto, it is all about proving that you can be a boxer - and still have a brain.
"Everybody has an impression of boxers that they, maybe, aren't too bright and there's not a lot of intellect involved," complains David.
"But when you combine chess and boxing, it brings the fact that you can be a fighter and still be a very intelligent person. It's going to show people that fighters can be smart people, or that smart people can be tough."
The sport has taken off in Germany. It is even being taught in a Berlin school, where they are busy preparing the next generation of chess boxing champions.
"My mum said I should learn boxing for self-defence," 10-year-old Aleg says. "I just love the way you can combine that now with chess."
Back in the ring, it is round seven and the players are locked in battle around the chessboard, sweat pouring onto their pawns.
Suddenly "Anti-Terror Frank" spots an opening and moves in for the kill. Queen to G7... checkmate!
The crowd erupts - the local hero has won and is awarded the world title belt. Which goes to show that when it comes to mixing brains and brawn, Germany really is the Grand Master.