Atardecer translates to "sunset." While it might seem common, its usage here is particularly evocative and beautiful, making it stand out.
In the song, Diego Torres sings about things that "florecen en secreto en el cielo pintado de cualquier atardecer" (blossom in secret in the painted sky of any sunset). It's a poetic way to describe where unspoken words and hidden feelings go, painting a vivid and romantic image that is both memorable and unique to the song's reflective theme.
"Donde Van" ("Where Do They Go") keeps asking the same unanswerable question about things that disappear. Diego Torres opens with "Dónde van las luces que no duermen" ("Where do the lights that don't sleep go"), and from there the song follows hurt and memory into hiding places rather than big drama: feeling "se escapan por la espalda" ("escapes through the back") when no one is looking, and settling "para siempre en un rincón" ("forever in a corner"). The chorus turns the question toward another person: "A dónde van tus sueños? Yo quiero ser el dueño" ("Where do your dreams go? I want to be their owner"), and closes on "El tesoro más preciado guardaré" ("I will guard the most precious treasure"). It reads less like a song about being loved than about wanting to keep watch over someone else's inner life.