Hey, what are those blue windows under the movie Enterprise, anyway?

The best look that you have at them is in the “vanity shot” in Star Trek the Motion Picture, where the camera rotates around and goes below the engineering section.

The answer is that they are the USS Enterprise’s arboretum or botanical gardens, a huge cathedral ceiling section of the ship containing tall trees and a botanical garden (the “shapes” in the windows are pine and oak and other trees). Psychologically, the purpose of the arboretum was recreation, and a relief from the stifling monotony and claustrophobia of shipboard life in space. But the arboretum served other functions, like oxygen generation and botanical research. The arboretum was clearly identified in Mr. Scott’s Guide to the Enterprise by Pocket Books.

From the tech manuals, we learn the arboretum has a snack bar and a pool for tropical fish.

The pre-refit original series Enterprise also had an arboretum that was seen on a few episodes, as did the Next Generation Enterprise.