Instructables member KlockworkKevin made a generator attachment for his bicycle. Even though he mostly used scrap parts for the generator, he was able to avoid making the whole thing an eyesore by hiding it in plain sight. When not in use, the generator is neatly hidden under KlockworkKevin’s patio table:
When he’s ready to burn some calories and charge some batteries, he just flips the table on its side and attaches his bike:
Here’s a demo of the generator (turn your volume down before you play it):
Wouldn’t it be awesome if all gym equipment worked like this? Head to Instructables to read KlockworkKevin’s walkthrough.