Contrabass valve trombone. Nominal pitch: 18-ft B♭.

https://images.is.ed.ac.uk/luna/servlet/iiif/UoEart~2~2~78634~186437/full/,150/0/default.jpghttps://images.is.ed.ac.uk/luna/servlet/iiif/UoEart~2~2~78421~186438/full/,150/0/default.jpg