Power Ring Grotto

The Power Ring Grotto is a location bordering Robotropolis which was a source for Power Rings.

Super Sonic vs Hyper Knuckles
Knuckles, worried that the Floating Island would be doomed if something happened to its only Chaos Emerald, decided to obtain another emerald. Using the Book of Myths, he found the ring grotto on the outskirts of Robotropolis. Sonic appeared and both engaged each other in combat. During the struggle, Sonic lifted a tree to hit Knuckles when Sally stopped the fight. They discovered a zone filled with Power Rings and Chaos Emeralds and Knuckles dived straight into it. Sonic followed and gathered enough rings and emeralds to become Super Sonic. Knuckles responded by repeating the process and becoming Hyper Knuckles and they resumed fighting. When Super Sonic and Hyper Knuckles collided at an incalculable speed, the zone collapsed, but not before it spat out Sonic and Knuckles. Sonic returned to Knothole Village with Sally, while Knuckles returned to the Floating Island with a Chaos Emerald in hand.

Powering The Death Egg
The Power Ring Grotto was sucked completely dry of power rings when Dr. Ivo Robotnik used the Death Egg to pull its contents aboard. The surrounding area, including garbage and trees, were also pulled up accidentally by the SWATbot controlling the procedure.