How to Discover
Look at the list of undergraduate majors.
Use the Advising Directory to review requirements of different majors and to find contact information for advisors in major departments. Print out the list of UM degrees offered and cross off the ones you know you're not interested in. If you can narrow it from over 50 down to 5 or 10, you've accomplished something. Follow the links for information about the remaining majors, including admission and graduation requirements, to further investigate. Then, look at which Exploratory Track has the most overlap with the programs you are interested in.
Use the Exploratory Tracks to help narrow down some courses and plan your schedule.
Each Exploratory Track contains recommendations for building your course schedule for the first three semesters along with a list of general education and introductory courses for the various majors in the Track. Select courses that interest you, while considering where those courses fit in with the General Education Requirements (GERs). If you decide not to declare one of the majors in that Track, those will still count towards your GERs.
Talk to people involved in the majors you're interested in.
Discuss your areas of interest with departmental or professional advisors, faculty members, and students already declared in those majors. Consider visiting or joining an ASUM student group, particularly one related to the majors you're interested in. You may also want to run any of your ideas by family and friends.
Make an appointment to speak with a career counselor in Career Services.
Although majors and careers are certainly not the same thing, the same skills that make career counselors good at helping people find their career passion might be directed to help you find your academic passion. Go the Career Services to see what they can do for you. Take a look at Career Services "What you can do with a major in..." series to find out what you kinds of careers you can have with various areas of study. Their office also offers the career assessment tools which may also shed light onto your academic interests. You may learn something new about yourself, may confirm what you already knew about yourself, or perhaps see things from a different perspective. In any case, it is fun to hear the interpretations.