My 2000 puzzle design is Watson's Wormhole, (Copyright Martin H. Watson, 2000. Production of this
design is only permitted on a single basis for personal use only. Please
contact me for commercial production license, for a 5x5x5 cube with a 1x1x5 void between the centres of two
It has a single solution and is very difficult. As yet, October 2001, I am not aware of anyone who has ever solved it manually. It consists of 12 pieces, each formed by joining pairs of planar pentacubes to form non-planar decacubes. Thanks to Rick Eason, Leonard Campbell and Steve Strickland for their analysis work, in confirming that it has one solution, and to Pat Hamlyn for providing initial solutions for filling half a cube.
Pictorial Assembly Instructions are here.