I joined a class with structure and discipline, specifically karate. There is a culture in karate of being respectful to your Maestro and also treating the class with respect. If I can not come I am expected to send a message to my Maestro telling him I will not be there. Being late is frowned upon, regular participation is expected. Of course this is real life and he understands is someone is late due to work or childcare issues, gets sick or has a social engagement. But for the most part my presence is expected and I like this little mbit of mental pressure to get me there even when I don't feel like it.
It is a great combination of athleticism and a good work out but also a peaceful experience for the mind.
I really recommend karate to anyone, of any athletic level, but, if it doesn't strike your fancy, why not think about signing up for a class of some sort where you are really expected to attend? Cooking? Group exercise? A language course or computer programming?