The main questline of level 23 finish there: you was supposed to enter in Caergate map and (just if you like) do some daily quests there.
Level 30+ can't enter any more in Caergate, so you can't complete that quest any more.
Same stuff will happen in level 39, when there is a quest to enter Viledon and talk to Selena, if you reach level 40, you can't complete it any more, because 40+ can't enter in Viledon.