The Roman building on the beach of Bacoli, identified as Agrippina's tomb in the nineteenth century, is actually a theater (probably an Augustan Odeion, similar to the one in Baia), converted to a ninfeo for water sports around the beginning of the second century AD because the effects of bradyseism meant that it was gradually sinking into the ground.
As so many of the ancient buildings in Italy, it was hard to find and in the end a little bid disappointing.
The surrounding structures have been lost, which make it difficult to work out the various transformations that have occurred over the course of at least three centuries. The theater was probably divided into three hemicycles; two upper, of the same size, and one lower. Even further down (about 1.30 below the level of the beach) a semi-circular board acted as the orchestra pit.