Vhnori death ritual

From Memory Alpha, the free Star Trek reference

The Vhnori death ritual developed amidst the presence of many naturally occurring subspace vacuoles on the Vhnori homeworld. They originally placed the bodies of the dead into these vacuoles believing that this would transport them to the Vhnori afterlife, called the Next Emanation.

Over time, this practice became combined with euthanasia. Vhnori citizens would enter a device known as a cenotaph that would kill them just before a vacuole opened.

Unknown to the Vhnori, the vacuoles actually led to a planet in the Delta Quadrant. On this planet the bodies of their dead had been piling up for thousands of years, resulting in the only known concentration of element 247.

All this was accidentally discovered by Harry Kim of the USS Voyager when he was accidentally drawn through one of the vacuoles to the Vhnori world in 2371.

He returned using one of the cenotaphs having seriously disturbed the Vhnori's faith. However, it was discovered that an unusual amount of neural energy existed in the planet's rings, perhaps implying that the Vhnori afterlife may not be completely without foundation. (VOY: "Emanations")