Harrogath is the town area of Act Five. Harrogath can only be entered by players who install the Diablo II expansion pack, Lord of Destruction, and it is accessed through a red portal opened by Tyrael, after a character defeats Diablo in Act Four.
Harrogath is a city in the frozen north, situated on the slopes of Mt. Arreat. It is located in the Barbarian lands, and all of the NPCs are Barbarians of one type or another, though they are hospitable to characters of other classes as well, once they've proved their worth.