A bathtub Madonna (also known as a lawn shrine, Mary on the half shell, bathtub Mary, and bathtub shrine) is an artificial grotto typically framing a Roman Catholic religious figure. These shrines most often house a statue of the Blessed Virgin Mary but sometimes hold the image of another Catholic saint or of Jesus.

While often constructed by upending an old bathtub and burying one end, similar designs have been factory produced. These factory produced enclosures sometimes have decorative features that their recycled counterparts lack, such as fluting reminiscent of a scallop shell.