Plen-an-gwary

A plen-an-gwarry or plain-an-gwary (), is a "playing-place" or round, a medieval amphitheatre found in Cornwall. A circular outdoor space used for plays, sports, and public events, the plen-an-gwary was a Cornish variant of a construction style found across Great Britain. Formerly common across Cornwall, only two survive nearly complete today: the "Plain" in St Just in Penwith () and Saint Piran's Round near Perranporth ().
The theatre area could be used for local gatherings, sports events, and production of plays. Cornwall culture had a type of play called miracle plays, written in the Cornish language, that were meant to spread Christianity. To capture the attention of the audience, "the plays were often noisy, bawdy and entertaining." The most important work of literature surviving from the Middle Cornish period is "Ordinalia", a 9000-line religious verse drama which had probably reached its present form by 1400. The "Ordinalia" consists of three miracle plays, "Origo Mundi", "Passio Christi" and "Resurrexio Domini", meant to be performed on successive days. Such plays were performed in a plain-an-gwarry.
St Just-in-Penwith.
St Just's plain-an-gwarry is a large circular space, encircled by a wall of stone. There are two entries into the space. In November 1878 the ″Plane-an-Guare″ was restored under the guidance of several gentlemen including William Copeland Borlase. The outer wall was exposed and several loads of stone were brought up from Boscean. By December 1878 the ″renewal″ of the outer wall was almost complete. The restoration was funded to provide relief for the unemployed due to the closure of local mines. It is central to the celebrations of the annual Lafrowda Day festival.
Perran Round.
Perran Round in the parish of Perranzabuloe, between Perranporth and Goonhavern is considered to be the best surviving example of a plen-an-gwary. 
Other sites.
Depending on sources there are a possible 48 to 51 plen-an-gwarys including nine sites with extant remains and a further nineteen sites with no above-ground remains. The possible sites are based on place-names.