The Ring Containers have no specific form. Instead, they come in various, medium-sized sized objects. This can include wooden barrels, fruit baskets, cave crystals, wooden frame crates, pots, brown sacks, etc.
In Sonic and the Black Knight, Ring Containers can be encountered throughout the various Missions in Adventure Mode. Their appearance depends on the area they are in: Camelot Castle's Ring Containers take the form of baskets and barrels, Crystal Cave's take the form of purple crystal formations, Great Megalith's take the form of wooden frame crates, etc. In gameplay, their purpose is to bestow the playable character with Rings. They do this when the playable character touches them, although upon doing so, the Ring Container will be destroyed, much like modern Item Boxes.
Most Ring Containers only grant one Ring. However, there are a few significant ones, like brown sacks, which can grant five, ten, or even twenty, Rings. Also, when bestowing Rings to the playable character, an icon representing the amount of Rings given will appear on the HUD.