My special interest is music. But it takes on many different forms - playing several instruments, composing songs on them, recording and mixing those songs, collecting records and CDs, cataloguing them, recording records on the computer and removing all the noises until only the music is left, making CDs of those remasters, designing and printing CD covers for them, and so on.
So I don't do one thing all the time, but I do a range of the same related things all the time, to the exclusion of other things, like watching TV or being interested in sports or politics or fishing or celebrity culture or cars... you know, guy stuff.