Dirt Mounds can be found in the course of exploration in Divinity Original Sin 2
Look for terrain or dirt that looks a bit different from the surface around it. It often looks like an elevated pile of sand or mud.
Use a Shovel or some other digging tool to dig the mound and find what's under it. This can include:
- Hidden Entrances
- (219,270): Outside of where you first entered Fort Joy, there's a long broken wall. At one point there's a path leading up to it. On top is a bedroll (and a rolled up version which is portable) and a shovel.
- Make sure to interact with the mound using the character that has a Shovel in its inventory.
- Lizard characters can dig without needing a Shovel.