Many Wraiths (7) + Ekimmara (11).
Monster Dens
Locations on Velen / Novigrad
1
Dragonslayer's Grotto
Related quests: Scavenger Hunt: Griffin School Gear
2Monster Den
There is golem (19) here.
3Monster Den
Many Nekkers (18) + Rabid rock troll (16).
4Trolls' Cave
Related quests: A Deadly Plot
Nekker Warriors (6) and Nekkers (6).
Locations on The Skellige Isles
5
Monster Den
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6Monster Den
Alghouls (21,23).
7Monster Den
Wraiths (29) and Katakan (29).
8Monster Den
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9Monster Den
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10Nekker's Mine
Nekkers (6) and Nekker Warrior (12).