In the quest “A Most Intriguing Invitation” one of the listed quest rewards upon completion is the portal to Dornogal. This is not a reward for this quest but for completing the entire quest line.
This is not made clear anywhere in the game. It does not say “questline reward” nor does it continue to list it as a reward for the next quest in the quest line, it just disappears from the included rewards. This would lead any reasonable person to believe it is a reward for the quest.
The only way to find out this is not the case is through a wowhead comment on the page for this quest. There is nothing to indicate this to players in game. This is poor UX design and should be made clearer so players don’t waste time searching the zone for the portal.