Bone-Eater's Well

is a well found in the shrine that Kagome lives at in the present day it is hidden inside one of the buildings of the shrine which is usually kept locked up. In the Feudal Era it is located in a small forest clearing; the well is used to dispose of bodies of demons and monsters but it also has the purpose off been used as a gateway between the present day and the Feudal Era.

Part in the story
The well is just like many usual wells in the Feudal Era, except that the well possessed an ability to connect the present era that Kagome comes from with the Feudal Era. How the well is active is currently unknown, but several aspects of the well can be deciphered based on observations made throughout the story: It can be presumed that only certain beings may pass through the well; a number of objects have the ability to as well.
 * The only human that is able to travel through the well is Kagome.
 * Inuyasha can travel through without any need of the Shikon Jewel; it is mostly because of his connection to Kagome that allows him to move between the two eras of time.
 * Neither Sōta nor Shippō are able to pass through the well; however, Sōta's voice could reach Inuyasha for unknown means while Shippō no success what so ever.
 * Mistress Centipede was killed and sent to the present era without any need of the jewel; it is suggested that demon's bones can pass through the well. In this case, Mistress Centipede was revived because she was near the Shikon no Tama (which was still in Kagome's body, unbeknownst to her).
 * Yura was able to send her hair to wreak havoc in the future; most likely because of the jewel shard she stole.
 * Both Sō'unga and Saya were able to pass through without the need of the jewel.

Uses
In the InuYasha franchise, The Bone-Eater's Well is a mystical well used initially to dispose of the bodies of demons and monsters, whom proved near unbeatable (that is, Mistress Centipede due to her constant resurrection). The Bone-Eater's well is a major aspect in the series due to its ability to act as a portal between the past and the future. This is obviously invaluable to Kagome who transits via the Bone-Eater's well to go to the Feudal Era and back, (as well as Inuyasha). Although other demons can also travel through the well too, such as Mistress Centipede.

Known users of the well
The demon's bone was sent to the future fifty years before the story start by Kikyō and her followers. She was able to resurrect herself, thanks to the Shikon no Tama and return to the past via the same well.
 * Mistress Centipede

Sō'unga was perhaps the very first object that traveled through the Bone-Eater's well. The sword was sent to the future 250 years before the story along with Saya.
 * Kagome Higurashi
 * Inuyasha
 * Sō'unga

Trivia

 * During both manga and anime, Kagome can go between both eras without the jewels' power. However, she needed it after Inuyasha temporarily forced back home in "Go Back to Your Own Time, Kagome!".
 * Shippō had the jewel's power and is a demon. However, he didn't go through the well.
 * Anything taken by Kagome and Inuyasha when the jump into the well comes out with them on the other side, such as Kagome's bike and bow from Mount Azusa.
 * In the final episode of the series when Kagome returns to the Feudal Era permanently, it remains unknown if she can still pass through the well anymore.
 * Apparently, some characters in the story had refered to the well as  possibly a living thing.

食骨之井