I don't fly 121 and am low-time, but FWIW, I landed at the wrong field once in a CRJ sim with a classmate doing a visual approach. We wanted to land at KSLC, and had the ILS tuned, identified and verified. We failed though. Foolishly enough, we landed at some other airport (can't recall the name) which had an identically numbered runway, and which ALSO happened to have a nearly identical ILS. Both airports were nearly aligned with one another too, so the localizer didn't indicate an error when the frequency was tuned in. We landed on it and then noticed that we landed at the wrong field, doh! It was laughable, but I'm glad that it happened to us in hindsight. If we had just given heed to what we didn't question, we would have caught our gaffing mistake in advance.
Our instruments were telling us that the distance to the airport was 20 miles away, and our glideslope was not functioning at all. Unfortunately since both airports are so closely aligned, the localizer was pegged dead center. We chose to ignore those other indications because the sim in which we were assigned annoyingly had a tendency to behave erratically all too often. That was our first big (and dumb) mistake. Making things worse, we should have noticed before we landed that the airport also looked different from the air. Maybe we could have gone around..