Denver has been changing so fast that anything I would have considered a "hidden gem" five years ago probably no longer qualifies. So I'll go with another city I know and love...
Rome's Rose Garden, situated just above the Circus Maximus on the Aventine Hill became one of my favorite places in the city. It is peaceful and hauntingly beautiful, having been the site of the city's Jewish cemetery prior to its relocation during WWII. In the 1950s, it was turned into the rose garden and its paths laid out in the shape of a menorah.
