Everyone knows them, only a few can solve their puzzle: Rubik's Cube.
Dealing with them properly takes a lot of practice.
The participants at this year's German Nationals, a kind of German championship of the speedcubing scene, which is organized by the World Cube Association (WCA), have that.
The best of them take between five and eight seconds to solve a randomly twisted standard cube.
Arriving in the Saalbau BiKuZ in Frankfurt's Höchst district, the visitor is greeted by a symphony of constantly clicking Rubik's Cubes.
The players, mostly under 25 years old and male, practice difficult moves again.
For a number of years, he has observed a steadily growing enthusiasm for the sport, especially among young people, says co-organizer Wilhelm Kilders.
But among the participants were also a few men in their 50s who, unlike the others, must have witnessed the first heyday of the Rubik's Cube invented by the Hungarian civil engineer and architect Ernő Rubik in the 1980s.
So does Roland Frisch, known in the scene as "Freshcuber".
The 55-year-old cube solver is actually a tram driver.
But he also runs a YouTube channel and a website where he gives tips on how to solve the cubes quickly.
He said he was already tinkering with the cubes in the 1980s when they were fresh on the market, but not for a long time.
He has been shooting again since 2015 and has been taking part in tournaments such as the German Nationals since 2016.
As Frisch says, there are different tactics for solving the cubes, says Frisch.
Beginners start with the layer-by-layer method.
Here you first try to form a cross on the white side of the cube, then the corners are rotated correctly.
Then the so-called second level is solved: The four edge stones in this level are placed in the right place.
The fourth step is to create a cross again on the last side, usually the yellow one, and then correct the position of the edge and corner stones.
The more advanced and also the most common way of solving the cube is the so-called CFOB method (Cross, F2L, OLL, PLL).
This is more complicated, because after the white cross (Cross) corner and edge stones are brought to the right place at the same time.
This step is called F2L, an abbreviation for "First two layers", because after it the first two layers of the cube are solved next to the white side.
Then comes the step in which the last, mostly yellow page is solved.
This is called OLL, which means "Orientation of the last layer".
Now only the edges and corner stones of the third level, which are often incorrectly positioned, are missing, which are correctly positioned by the last step PLL (“Permutation of the last layer”).
For each of these steps there is a series of sequences of moves, so-called algorithms,
to learn and train.
For the third step alone, the OLL, there are 57 different algorithms to learn, says Frisch.
For the PLL, it's 21. Once these move combinations are in place, players would need to practice what's known as "look-ahead."
This means knowing already during a sequence of moves what the next move and the move after that will be in order to minimize the time between moves.
In addition to the classic and well-known 3x3x3 cube, there are other disciplines such as the two, four, five, six and seven cubes.
The program also includes solving the dice with one hand or blindly.
For Wilhelm Kilders, who has been solving Rubik's Cubes for more than ten years and often moves around the ten-second mark, the "multiple blind" discipline is the most demanding.
For one hour, players look at as many twisted 3x3x3 cubes as they dare to solve blindly.
They then blindfold and solve the cubes one after the other.
Once someone solved 25 cubes in a row, he says.
The favorites for the final in the classic discipline, solving the 3x3x3 cube on time on Sunday, are the brothers Philipp and Sebastian Weyer.
The former solved the cube in just under six seconds in one round.