Music
I am continually fascinated at how music can change or amplify a mood. There are certainly numerous examples of that but I always find that the band Hammock is exceptionally effective at being able to do exactly that. This is particularly true with their Departure Songs album.
If you listen to Departure Songs on a gloomy weather weekend day (like today) it seems to meld perfectly into the mood.
Someday I would like to study how music can affect us this way and I wonder if it is some sort of resonance with brain waves or some other physiological reaction in the parts of your brain tied to hearing. I would always like to hear from my friends that have made a career out of music and what they think about what makes music so impactful to us.