Finding all the Monster Nests in The Witcher 3: Wild Hunt will allow you to unlock two Achievements/Trophies plus one in-game bonus. Those are “Pest Control (30 Gamerscore / Silver Trophy) — Destroy all monster nests in the Velen / Novigrad region, or in Skellige, Fire in the Hole (15 Gamerscore / Bronze Trophy) — Destroy 10 monster nests using bombs, and Bonus: You receive 20 Experience Points for each Monster Nest you destroy.
There are 25+ Monster Nests all around The Witcher 3: Wild Hunt map. It is preferable to start with Skellige, since you will find only 5 Monster Nests over there, unlocking “Pest Control” very fast. 4 of those are on the main island (Ard Skellig) and 1 on the northern island (An Skellig). You can destroy Monster Nests with bombs like Grapeshot or Dancing Stars.
This is the timeline in minutes for the Monster Nests Location Guide in Skellige:
Monster Nest Location #1 – Ard Skellig – 0:05
Monster Nest Location #2 – Ard Skellig – 0:33
Monster Nest Location #3 – Ard Skellig – 0:56
Monster Nest Location #4 – Ard Skellig – 1:26
Monster Nest Location #5 – An Skellig – 1:56
Velen & Novigrad together have over 20 more Monster Nests. Remember to save after you burn each Monster Nest, as the game won’t do it automatically for this.
After you destroy a Monster Nest with some items you need, simply leave one item and walk away to come back a second later: all items in the Monster Nest will be restocked! You can keep doing this up to around 20 times.