Antichron's elegant symmetry - it has the group consisting of the three half rotations around each axis - make it a favorite with mathematicians and the rest of us alike.  This instance is bronze mounted to a base of marble and cocobolo wood, 8" tall overall. 

In February 2002 I helped carve this piece as a snow sculpture 12 feet tall, under the name A Twist in Time.  The team also figured out that it is homeomorphic to a Klein bottle with one handle added and two disks cut out. The homeomorphism remains to be exhibited.