You can destroy Monster Nests just like in Witcher 2. Crafting or Buying Bombs and using them on the Nests. 

In the Witcher 3 it works the same way you have to blow up the nests but with some new twists. Before you would go to the nest and press a button to drop the bomb.

Now in the Witcher 3 you can throw a bomb towards the nest or use a destructive sign at it to destroy it (You can try **Aard** or **Igni** (will try to confirm Igni on some nests later)).

> "look around the chamber until you spot the two smoking mounds lying
> either side of the pit. As instructed, use either bombs or one of your
> destructive spells to obliterate them" **- Quote from Guide**

The specific bomb to destroy nests in the Witcher 2 was the **Grapeshot Bomb**