boudica: There are level brackets for Quest Units:
1-19
20-39
40-59
60-79
80+

To find a Quest unit for your level bracket, go to your Home page. Then click on the Quests icon. It will show you what Quest units are available & where they are located. If you are at level 19, 39, 59 or 79 you need to know that you may pop your level up to the next level bracket & you can no longer fight the Quest unit that you were just now fighting. It happens sometimes because Quest units give good experience. The End.