Remember when you were a kid, and could play a pick-up game of basketball with your friends or (after a little begging your parents) sign up for any of dozens of sports? Those days don't have to be behind you. There are lots of sports and activities that are open to us grown-ups. Here are a few.
In making the list, we chose sports and activities that are accessible to people with little or no experience. We also left off some of the obvious things, like running, weightlifting and yoga, because you already know you can just go do those any time.
Most of these also come with some sort of community -- either you're on a team, or interacting with a group of regulars. And since the best workout is the one you like (because it's the one you'll actually do) having buddies is a major help to your fitness.
Indoor bouldering is probably the easiest form of rock climbing to get started with. You don't need ropes or a partner, and you won't be going very far off the ground; the challenge is to climb along a marked route without falling off. Of course, once you start hanging out at climbing gyms, you may make friends who will rope you into other types of climbing. Here's a list of climbing gyms.
Social dancing makes the "solo" list because you don't need a dedicated partner, although bringing a buddy can provide a psychological safety net. Get started with a combination of taking lessons and just going out to dances. To pursue dancing as a sport and hobby, see if you can find a group of dedicated dancers who hold practice sessions and go to workshops. I'm partial to lindy hop, a form of swing dancing, but you can find similar communities built around salsa, tango, and many others.
Circus arts provide physical and mental challenges. Aerial silks classes are available in many cities (you'll climb and twist in fabric suspended from the ceiling) but you may also be able to find a circus school offering classes in other skills like unicycling and trapeze.
Traditional And Unusual Team Sports
You can play almost any traditional team sport on a recreational basis. Google your favourite along with your location and words to the effect of "adult leagues" and you may find just what you're looking for. From netball to cricket to soccer to softball, chances are you'll find teams keen to sign up new members.
Roller derby, available for men and increasingly for women, is a full-contact sport played on wheels, although more often on flat ground than banked tracks. Leagues tend to be tight-knit social groups, amping up the addictiveness factor. The Derby Roster lists competitive leagues worldwide. Some also offer no-contact or less-contact recreational programs.
Adapted from the pages of Harry Potter, Quidditch is a real sport played without magical spells. (The snitch, instead of being a flying golden ball, is a ball carried by a neutral player dressed in gold.) Check the Australian Quidditch Association for details.
This is only a starter list, so tell us in the comments -- what fun sports did we miss?