The sense that lets you touch your nose in the dark.
Muscle spindles, Golgi tendon organs and joint receptors constantly report length, tension and angle. Charles Sherrington coined the term proprioception in 1906 for stimuli arising from the body itself. Ian Waterman lost this sense from the neck down to a viral infection and had to steer every movement by sight.
Useful: Without it, walking would be a task demanding your eyes' full attention.
Source: en.wikipedia.org