squirrel cage

Short definition from Wiktionary

Noun

1. 1
   A circular cage for a squirrel or other small animal, which rotates vertically as the animal runs at the bottom.
2. 2
   A tedious, repetitive, unfulfilling activity or situation, especially one in which no progress is achieved.
3. 3
   Any other device, such as a fan or rotor, that resembles a squirrel cage in form.