Amphitheater

[Agnes]

a circular or oval area of ground around which rows of seats are arranged on a steep slope, for watching plays, sports, etc. outside

[Mark Zuckerberg]

a large hall for lectures in which the rows of seats are arranged on a slope

[Tina]

(especially in Greek and Roman architecture) an open circular or oval building with a central space surrounded by tiers of seats for spectators, for the presentation of dramatic or sporting events.