"Ode on a Grecian Urn" has two settings: the speaker’s world and the world of the urn.
Compared to the fantasy on the urn, the speaker’s world feels small and intimate: it consists of the urn and himself. You could imagine he’s out to dinner with the urn at a softly lit restaurant, or maybe rollerblading in the park. But we think he’s most likely viewing an urn at the British Museum, or in someone’s private collection. Even apart from its decorations, the urn has a smooth, beautiful shape, as the poem notes in line 41. There are at least three images depicted around its circumference: one with randy guys chasing a beautiful women, another with a young man playing pipes under a tree, and the third showing a cow being led by a priest to be sacrificed. These images are "fringed" or bordered by a decorative pattern of leaves (line 5).
The world of the urn is entirely pastoral, as the poem notes in line 45. The Ancient Greeks were big on pastoral imagery because most of them lived in small towns or on farms, and almost everyone depended on local farmers for food. The Greeks lived (and still live) along the Mediterranean Sea, which was great for crops but not necessarily for big trees and forests. But the urn seems to have a lot of trees, which leads the speaker to guess that it is set in "Tempe or the dales of Arcady" (7), which were known for being especially lush and green parts of Ancient Greece. There are so many references to leaves, trees, and other green things that if the urn were a real place you might have to hack your way through it with a machete. Flowers and vines are wrapped around everything, including the people (depending on how you read lines 42-43). It’s an eternal spring, and the trees will never lose their leaves.
Moving through the poem is like walking through a dense forest of language. Every time we encounter a new scene, it’s like stumbling on a clearing with people in it. In the first clearing, there is music playing, laughter, and half-naked couples running around. It looks like a party. Before coming into the second clearing, we hear the piercing sound of a solitary pipe. This is the young musician under the branches of a huge tree. (Or maybe he’s just off to the side of the scene with the couples, but the poem implies some kind of separation.) The third clearing is actually a path leading to a forest altar. We have no idea where the nearest town is, but all these people must have come from somewhere, so we have to invent one in our minds. That cow looks pretty unhappy, and it won’t stop mooing.
The poem ends by returning to the original setting of the speaker, but this time the speaker falls away. It feels like we’re watching the security videotape at a museum on "Fast Forward" mode, except stretched out over years and "generations." We see new people rushing in and out of the room. They crowd around the urn and try to figure out its mystery by talking to it. After the urn delivers its timeless message, they scurry out again like mice and are replaced by a new generation of people. It delivers the same message every time.