The key is to try new things. Don’t just look at something and say, “Is this my passion?” You need to experience new activities.
A great place to research volunteer, hobbies, and work activities is the Internet Public Library. The categories are organized well and easy to scroll down. Under Arts and Humanities, there are fifteen sub-headings that range from Classics to Philosophy to Language.
In the History Sub-Heading, a quick scroll took us to The George C. Marshall Foundation. “Biographical information, interviews, essays and research materials about General George C. Marshall and World War I." Obviously, this isn't for everyone, but an indication of the breadth of resources available.
Take a look at the site, what is has to offer and start exploring what you want to do next.