Rubik's cube

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 and was able to solve it. (DW: The God Complex)