Superflip
The superflip or 12-flip is a Rubik's Cube configuration in which all 20 of the movable subcubes (or "cubies") are in the correct permutation, and the eight corners are correctly oriented, but all twelve of the edges are oriented incorrectly ("flipped"). It has been shown that the shortest path between a solved cube and the Superflip position requires 20 moves under the usual half-turn metric (HTM), and that no position requires more moves (although, contrary to popular belief, there are many other positions that also require 20 moves). Under the more restrictive quarter-turn metric (QTM), the Superflip requires 24 moves, and is not maximally distant from the solved state. Instead, when Superflip is composed with the "four-dot" or "four-spot" position, in which four faces have their centers exchanged with the centers on the opposite face, the resulting position may be unique in requiring 26 moves under QTM. (Wikipedia).
