According to the author of the article Frank Gehry, Guggenheim Bilbao, what do the walls of the museum resemble?

Answerbarrel vault

Relief sculpture - images are set against a flat background. a coin is a good example: the inscription, the date, and the figure are slightly raised above a flat surface. the ancient egyptians sometimes carved figures into a flat surface.    pro: they take significantly less time to make and do not require as much tools or skills as free-standingcons: not nearly as realistic, as it is not fully 3-d, and does not have the details that a free-standing one does.freestanding sculptures (also called  carved in the round) are not attached to any  background.  they are 3-dimensional  and fully rendered.

It depends on what picture your taking