Rubik's cube
From Tardis Wiki, the free Doctor Who reference
A Rubik's cube was a toy that was popular in Earth in the 1980s.
Luke Smith owned a Rubik's cube that he kept on his bedside table. (SJA: The Nightmare Man)
In 2011, the Eleventh Doctor toyed around with a Rubik's cube he found in George's bedroom and was unable to solve it. (DW: Night Terrors) He later found one while in the hotel constructed on the prison ship. (DW: The God Complex)
