Gates of Hell is an anime-only swamp.
Flora and Fauna
The forest appears to be a vast area of tropical swamps with dense trees completely blocking the sky and widespread deep canals and rivers. Its wildlife varies from climber monkeys, numerous leeches to swamp alligators and Toco toucans.
Team Fairy Tail A was sent an a mission by Laxus Dreyar to the forest in order to bring him a Magic Stone. There the Mages encounter several animals, Lucy picked on by leeches, Gray harassed by monkeys and Erza assaulted by alligators. Eventually, a monkey gives Gray the said stone, thus completing their quest.