I have a tradition on All Hallows' Eve & Samhain. I do my best to marathon through as much of the series as I can.
Also I get the urge to weild a whip when there's a clear night with a crescent moon shining down on me.
Ah! Samhain is the BEST time for CV. When the veil between the worlds is thinnest, as are the walls of the Castlevania. Any and all Castlevania will do then!
Thunderstorms, winds, massive rainfall, all set the mood for CV. Sometimes I read things in Latin or Romanian or look at Ayami's splendid artwork, that puts me in a great vampire-hunting state. Organ music, choirs, they send shivers down my spine and then I just HAVE to take up the whip! That is why Symphony's soundtrack leaves me enraptured and I can play it for a long time and usually do.
I like playing Lament of Innocence around Lammas because of the story of sacrifice surrounding that time (August the first.)
And Order of Ecclesia whenever I feel oppressed. Shanoa is a character I can relate a lot to.
Otherwise, when there's a chill in the air and a full moon shining bright, the only light coming from my TV screen... it's time for my inner vampire huntress to emerge...