I am self-taught on the harp. I first got interested in it on a tour to Mexico where I picked up a small folk harp during the mandatory tour of music shops. This works very well in the context of medieval music. It plays diatonically, so has to retune if adjacent pieces are in different keys.
A couple of years later I bought a larger folk (Celtic) harp in London so as to be able to use the lower register. This one has little movable levers so I can sharpen each string individually by one semitone. This makes it easier to change key from one piece to the next. I have played these harps quite a bit in theatre, as the sound decays quite quickly making it suitable to accompany text.