History, particularly from the Victorian Era to the interwar period after World War I. My grandfather has a hoard of old objects of our family from just that period, rings, jewelry, clocks, pictures, documents (land deeds, diary pages, etc. All mostly in Swedish, in near perfect conditions with even the coats of arms on the wax seals and everything still legible.). It's probably just this collection that got me fixated on history in the first place.
Also, English as a language is another lesser object of fixation for me.