steampunkvehicles:

Some deep, DEEP digging has revealed this photo of the sociable monowheel or tandem unicycle, from the sale catalog when the Canberra Bicycle Museum closed in 2008.  I have seen this in person and it is life-sized. 

Item: Sociable Monowheel for two characters; confuses the hell out of anyone following you but requires both players roll for Dexterity.