What is the setting of "Rip Van Winkle"? What feature of the place seems to be the most memorable? What details suggest when the story takes place?...

At the beginning of Washington Irving's tale "Rip Van Winkle" the narrator offers a description of the story's setting by detailing geographical features

WHOEVER has made a voyage up the Hudson must remember the Kaatskill mountains. They are a dismembered branch of the great Appalachian family, and are seen away to the west of the river, swelling up to a noble height, and lording it over the surrounding country. Every change of season, every change of weather, indeed, every hour of the day, produces some change in the magical hues and shapes of these mountains, and they are regarded by all the good wives, far and near, as perfect barometers.

In this opening sequence of sentences, Irving indicates that the story takes place at least near "the Hudson" river and "Kaatskill mountains."  Furthermore, his emphasis on the "magical hues and shapes of these mountains," creates a background against which the story will take place.  

The narrator continues to "zoom-in" on the scene by describing "a little village of great antiquity, having been founded by some Dutch colonists, in the early times of the province...."  Thus, spatially the story is located in present-day upstate New York in a small, old village.  

As far as the time period is concern, Irving's indication that it takes place (at least in its beginning) "while the country was yet a province of Great Britain."  This political detail definitively places the time of the story before the Revolutionary War and, thus, prior to 1776.  

While determining what the most "memorable" feature of the setting is inherently difficult because it relies on individual readers' reactions, the space that to which Rip escapes from his wife,

a deep mountain glen, wild, lonely, and shagged, the bottom filled with fragments from the impending cliffs, and scarcely lighted by the reflected rays of the setting sun. For some time Rip lay musing on this scene; evening was gradually advancing; the mountains began to throw their long blue shadows over the valleys; he saw that it would be dark long before he could reach the village, and he heaved a heavy sigh when he thought of encountering the terrors of Dame Van Winkle.

This "wild, lonely, and shagged," glen serves as the setting of the story's pivotal scene in which he encounters strange men playing a game, falls asleep, and wakes up after the Revolution.