I see you wrote "alone if necessary". I'll explain what I did, even though it's hard to do alone, then bring up some related alternatives.
Pair dancing. I started with ballroom dancing. It's an easy start because at the beginning it's a matter of following rules. However, social ballroom is rare, and a lot of it heads towards competitive dance at the higher levels. (It's easier in a college as many colleges have a ballroom dance club.)
There are many folk-related dances (contra, Scottish country, etc.). These are almost always low-key and informal. They usually meet in the evening/weekend afternoons.
Salsa dancing is, I think, the most popular of the pair dances. Even small cities usually have a place to go salsa dancing. It's what got me to start going to clubs on a regular basis. Rueda is a related dance where pairs arrange themselves in a circle and follow what the caller does. That can make it easier, because you don't need to think of what to do next, and there's less need for a lead/follow connection. (Which takes time to learn.)
Salsa dancing also rarely starts before sunset. (You can dance to salsa alone, btw.)
Swing dancing is fun, and energetic. It's less common because it requires more room. A large numbers of dances fit under the "swing" category; blues is much less energetic than Lindy Hop.
Tango is the hardest of the dances I learned. It took some serious study even after learning a few other dances. I think of it as the most improvisational of the dances I know. That's also because my tango includes aspects of salsa and swing, but not really the other way around.
There are other dances as well, as I start to move away from pair dancing: country western, breakdancing, African dance, modern dance, Hindi/Bollywood-style, popping, Kizomba and (mixing now with martial arts) capoeira.
Some of those you can definitely do on your own, at home, as well as in a group.