The Gerdig UFO is a Slovak brainteaser invented by the engineer Gerhard Huncaga in 1991.

The puzzle has two layers that slide in relation to each other and eight spheres that are split in half in order to rotate with the two-layer disc. At the center of the disc is a button that can be pushed up or down, but only after you rotate the discs, to mix up the spheres. When you push this button, a sphere (or more than one, depending on the difficulty) is rotated 180º and each half is now at opposite layers.

After the puzzle has been all scrambled up, it's time to solve it. Here you'll have five choices regarding it's difficulty. At the back side of the middle button there's a screw that when opened, will reveal the mechanism inside responsible for rotating the spheres. You can manipulate it to allow one sphere to be rotated, two opposite spheres, four spheres in a cross pattern, two spheres separated by 90º and three spheres, also separated by 90º from each other. The first level is trivial to solve, but the others are a bit more complicated, where you'll have to think about a strategy to solve them.

In terms of appearance, the puzzle could look a lot more cool, perhaps if it were chosen a different color scheme. As it is, it kinda looks like a baby rattle. Not that there's anything wrong with that... Other than this, the puzzle is a lot of fun to play with and the different levels of difficulty add to it a great replay value.

You can buy the Gerdig UFO at Milan's Puzzles.