[Manj]

Zombies if you want Rank 1 Windmill immediately. At Rank 4, you need to kill 450 "Boss" monsters as well as 3100 "Strong"/"Awful" and fulfill the attacking multiple targets requirements just to have enough proficiency for rank up. So I guess Rank 4, you can do in the dungeons.

However, starting Rank 3, the requirements ask for 1500 "Boss" monsters and 1300 "strong"/"awful" monsters. At Rank 2, it asks for 2000 "Boss" monsters. You can do all of this in the dungeons, but I assure you it will be very lengthy and boring. Sure I guess it will be boring doing this in Tir Na Nog, but its quicker so you won't be as bored.

As your Windmill rank is higher, so is your power level. Finding "Boss" type monsters in common dungeons like Ciar Intermediate won't be easy especially during Rank 3 and Rank 2.

In fact, at Rank 2 Windmill and a certain age and level, you are at the borderline between Zombies being a "Boss" and "Awful" monster.