Swamps of New Horseleans

The "Swamps of New Horseleans" is a swamp located in Equestria near the Appaloosan Mountains and Gelding Grotto.

At one point in the past, the city of New Horseleans was founded in or near the swamp.

Behind the scenes
The swamp first appeared in the semi-canon comic in The Return of Queen Chrysalis story arc as a feature of Twilight Sparkle's map. The swamp is named after the real-life city of New Orleans