668.56 centimeters is equal to 263.58 inches.
To give a comparison, an average door height is around 80 inches, making 668.56 centimeters approximately 3.3 times the height of a door.
Another comparison could be the average height of a basketball hoop, which is 120 inches. In this case, 668.56 centimeters is about 2.2 times the height of a basketball hoop.
In terms of objects with similar lengths, 668.56 centimeters is about the length of an adult human femur bone and slightly longer than a standard guitar (which is usually around 101 cm in length).