On this page of the Valheim guide, you'll learn how to unlock the Obliterator.
The Obliterator is one of the objects added to the game in the Hearth And Home update. It allows you to destroy any object and get coal in return - simply place the desired object inside and pull the lever.
To build it you need iron, copper and a new resource - thunderstone. You can't obtain this resource while exploring. You need to purchase it from Haldor for 50 gold.
After buying the thunderstone from the merchant, the option of building an Obliterator will become available. You can place it by using the hammer, anywhere within the forge's range.