Undercity is also another explorable area from another mmorpg game, Guild Wars:Factions. The area is connected to the region of Kaineng City.
"Cantha is a nation of many, many people. The marketplaces are packed, the cities are overcrowded, and the sewers are overflowing with waste. Underneath the busy streets, the darker side of Cantha rears its ugly head. If you're looking to engage in unsavory activities, Undercity would be the place to come."