Spiro-pentane, or spiro[2,2]pentane, consists of two cyclopropane molecules that have been fused at one C-atom. Look at the molecule from different perspectives and note that the two cycolopropane rings are perpendicular with regard to each other. The coordination of the central C-atom is sort of tetrahedral but is is highly distorted since the angles in the rings are only about 60 degrees.