The cenotaph is a device used by the Vhnori to send their dead to the Next Emanation. A person who is near death is placed into the cenotaph, which terminates their life just prior to the appearance of a subspace vacuole, which in turn transports the body to a planetary ring system in the Delta Quadrant.
In 2371, Harry Kim of the USS Voyager was accidentally transported into a cenotaph on the Vhnori homeworld, through the same vacuole that transported Ptera to Voyager. He was able to return to Voyager by taking Hatil Garan's place in the cenotaph. (VOY: "Emanations")