Nightfall characters get there as part of the quest Honing your Skills. Kamadan is the starting point in Elona for characters arriving from other campaigns. To access Kamadan from the Prophecies Campaign, complete the quest Sunspears in Kryta, acquired from Lionguard Figo in Lion's Arch. From the Factions Campaign, follow through the quest Sunspears in Cantha instead, which can be acquired from Imperial Guardsman Linro in Kaineng Center. If you have all three campaigns unlocked on your account, either of these two quests (which are mutually exclusive) can be obtained and completed by any Tyria-born or Cantha-born character.