A realm in which events take place; an area of interest, study, behaviour, etc.
The sand-covered centre of an amphitheatre where contests were held in Ancient Rome.
An enclosed area, often outdoor, for the presentation of sporting events (sports arena) or other spectacular events; earthen area, often oval, specifically for rodeos (North America) or circular area for bullfights (especially Hispanic America).
The building housing such an area; specifically, a very large, often round building, often topped with a dome, designated for indoor sporting or other major events, such as concerts.
the biosphere
The portion of the atmosphere from sea-level to about 4000 meters in which it is possible to breathe without technological assistance.