Popular groups on campus include a cappella groups (there are something like seven), comedy troupes, VSA (the student organization), VICE (the music organization), Philaletheis (one of the student theater organizations), QCVC (Queer Coalition of Vassar College), and so many others. I personally am in one of the a cappella groups on campus, and we perform multiple times on campus throughout the year. I wish that the administration were a little bit more invested in the organizations on campus--funds seems to be always at a low--but for the most part, I'm more than satisfied with the way organizations are received on campus.
Students in the dorms will definitely leave their doors open if they're not busy working or sleeping or whatever else. There is a common misconception that Strong House, the all female dorm, is not as friendly or as social as the other dorms because it's quieter. This is not at all true. I lived there for two years and met my best friends there. Some of the greatest parties I've been to were thrown in Strong.
As they say on the tour, every weekend at Vassar, there are multiple things to do. This is 100{4a082faed443b016e84c6ea63012b481c58f64867aa2dc62fff66e22ad7dff6c} completely true. Guest speakers, programs, concerts, plays, performances--you can find just about anything. And students flock to them, for the most part. Everyone on campus really enjoys the things that Vassar has to offer, socially. The college throws some awesome parties throughout the year, too, like the Halloween party and the numerous balls/dances that the dorms organize, and they're always tons of fun.
At Vassar, there is often a "work hard, play hard" mentality. The weekend starts on Thursday nights, usually, because few students have class on Friday. Most parties take place in senior housing, though dorm parties definitely happen, too. Usually, people will start the night in their dorm with friends before heading out to senior housing later on in the evening. Once the weather gets nice, the parties will happen outside, and people will all congregate on the lawns between senior houses. Matthew's Mug, the dance club on campus, is always a hot spot during the week. Every night is a different theme (Tuesdays, Jazz Night; Wednesdays, 80s/90s Night, etc.), and people will often end their nights dancing it up with friends there. It's a staple on campus.