Ruin

Ruin is the fourth world of the future in The End is Nigh. It takes place in a acid filled sewer, and consists of 21 levels. It's inhabited by agonyias, agons, ferals, thistle fishes, retinaras and wailers. At the end of Ruin there's a giant sphere of energy with friend attached to it. Approaching it will trigger a cutscene and the Acceptance escape sequence.

The Ghosts and Grieving cartridge can be found there.