I think my favourite bizarre instrument is without a doubt the Siberian Cello-Horn. It's got the body resembling that of a cello, only with a hollowed-out neck and a double-reeded mouthpiece that one can play like a bassoon's.
And then it's got a few holes to be played with the thumbs on said neck to produce various droning tones while the rest of the instrument is played exactly like a cello would be. Only I think it's tuned differently and has one extra string.
Either way, the double used of the resonating chamber and the combination of sounds makes for an entirely eclectic and wonderful sound.
