Have the image critiqued first. Post it on 500px.com and see what happens. Or, as has been mentioned, take it to an art gallery and get an unbiased opinion.
Generally having just one image isn't going to be enough to sell. Places that accept work like stock agencies or galleries want large bodies of work, and not just a single image.
You can try selling the image on etsy, ebay and the like, but before spending a dime on this unbelievably special image, have the image critiqued. Either go to an art gallery or take it to a local professional photographer and talk to them about the image. Also note that images that look fine on your phone or tablet often completely fall apart when printed. Was the image made with a phone or a real camera? If it was with a phone, then it's likely that you'll be limited to prints no larger than 8x10 which is too small for most people who buy wall art.