The Skulk Expansion mod adds a new dimension called The Echoing Ancients. This dimension contains cave-like generation and new plant life. Void Moss and Petra Trees scatter the land. By chopping down these new trees, you can get the Petra wood set, as well as Petra Crystal blocks which are a new light source. Keep an eye out for new structures which contain precious loot; Ward Armor sets, and Echo Crates containing new Echo tools. There are new recipes and new items to try out.
But how do you get to this new dimension? Find new Skulk Explorer Villagers in cabins throughout the overworld. They will trade you an Ancient Gateway Portal Igniter that can be used to ignite the portals in Ancient Cities.... but make sure to sneak and quietly remove any blocks that may be obstructing the portal.
Have fun!
Love everything about this mod!