In my childhood I had a fantasy about an orchestra that features gigantic upright brass instruments, so imagine my surprise when today I stumbled across a real instrument very similar to what I had imagined. What a humongous tuba!!
I'd love to compose a grand symphony featuring this instrument... Unfortunately I can't imagine it being particularly agile, so it'd probably be mostly confined to playing long pedal notes. If it actually is agile, though, I'd love to hear it playing a ground-shaking bass melody in 16th notes... :-P