I tried to answer this question from the age of 21 to 24.
I had no idea what I wanted to do. I went to career coaches, read books on the topic, listened to motivational clips on Youtube, etc.
Then when I was 24 I read a book called "So good they can't ignore you"
This flipped my thinking completely upside down. It basically went on to say that if you ask people what they are passionate about, they will tell you, swimming, cycling, taking my dog to the park and eating Mexican with friends. These passions are not going to make a career. I highly recommend you read the book, it basically changed the way I look at my career.
In terms of finding new things I'm "passionate" about outside of work. I just went out there and tried them. I joined a hiking club, went to night school classes on cooking, took archery lessons, tried out skiing, got into road cycling, joined a property investment association. I didn't know these were my passions when I first tried them out, in fact I was very hesitant to. But these are now my passions and I wouldn't have found them sitting at home. You almost have to put yourself in uncomfortable situations to help yourself grow, develop and explore as a person.