The term “zoological” (zoo) originates from a combination of Greek words meaning “a place for the study of animals.” However, the reality of zoos is complex, serving as both entertainment venues and sites of divisive ethical debates regarding animal cruelty.

It's even more complex trying to imagine what happens to a zoo after it is permanently closed, leading to animals being transferred to other facilities or brought back to the wilds.

Images of abandoned zoos are rarely shared online, but we found 21 unique photos showing the surprising decay and environment swallowed by nature from places that were once brimming with animal and human life.