Invariably (about once a year, maybe less) a small aircraft headed
to FTG lands at DEN, 5 nm miles away, thinking it's FTG.

Now, DEN is Class B, has a tower ( BIG tower! ) parking lots that
are always full that strech for miles, lots of really big
aircraft, and that silly terminal with the white things sticking up.
Not to mention runways that are 150 ft. wide.

I'm astonished how they can be mistaken for each other.

We won't talk about the 737 flown by a major airline that almost
landed at FTG thinking it was DEN. Actually, wouldn't have been
much of a problem -- FTG runways are 8000x100.