A Nether city is a Nether-brick structure found in the nether. The Nether City is populated by Zombie Pigman, living on buildings of Netherbrick, typically in a lava ocean. Exploration can be dangerous, as a hit from a denizen of this city can send you fore a fiery swim. If you have a way to do it, fire resistance is heavily recommended.
Much loot can be found in these structures, such as gold, iron, and lapis blocks, as well as rare Netherwart. Some buildings contain a roller coaster, which can be fun - but be wary, the ride ends with a bang. Other buildings include a hotel-like structure, a nether-brick pyramid, and the Pig Mage's altar as well as smaller houses.
The Boss of the Nether City is the fearsome pig mage. He is not to be trifled with, as he deals heavy damage and can set you on fire.