Challenge Mission

From the Factions FAQ:

Challenge missions involve specific scoring objectives, such as holding out against progressive waves of enemies. The rewards may be experience, gold, and, for some missions in Guild Wars Factions, Luxon or Kurzick faction points, depending on completion and mission. You will see personal bests and high scores displayed within the game. In the Nightfall challenge missions it is possible to obtain the items required to obtain the items required to change heroes' armor art, the probability of obtaining these items is suspected to increase with higher scores, however it is possible to obtain them even with low scores.

Guild Wars Factions features the following challenge missions:
 * Dragon's Throat (Kaineng City awarding Gold)
 * Altrumm Ruins (Echovald Forest, awarding Kurzick faction)
 * Amatz Basin (Echovald Forest, awarding Kurzick faction)
 * Zos Shivros Channel (Jade Sea, awarding Luxon faction)
 * The Aurios Mines (Jade Sea, awarding Luxon faction)

Guild Wars Nightfall features the following challenge missions:
 * Dajkah Inlet (Kourna)
 * Remains of Sahlahja (The Desolation)
 * The Shadow Nexus (Realm of Torment)

In each of these locations, there will be Records NPC listing the current high scores.