amphitheatre

1. (geology) A natural formation of a similar shape, where a steep mountain or slope or particular rock formation forms a partial or complete bowl, especially one used as a performance space (and possibly modified by carving out seats, etc) because the slopes naturally amplify or echo sound.Examples: "The difference between the approach to Baylen from the west and from the east, is that on the former side the traveller reaches the town through a semicircular amphitheatre of upland, while by the latter he comes up a V-shaped valley ..."; "Brecon or Aberhonddu, a typical Welsh town of 5,350 inhabitants, stands in a grand amphitheatre of hills and mountains at the confluence of the rivers Usk, Honddu, and Tarell."