bottomless pit

Short definition from Wiktionary

Noun

1. 1
   A pit with no visible bottom and apparently infinite depth.
2. 2
   Hell.
3. 3
   An endless resource or supply.
4. 4
   A person with an apparently boundless appetite; an entity or problem which consumes seemingly endless resources.
5. 5
   An in-game hazard made up of a deep hole or void with no visible bottom, where falling in typically causes the player’s character to instantly lose a life.