Extended Caves aims to expand underground exploration by adding more realistic features and treasures giving the player a better experience below the surface. You’ll almost immediately notice a difference with the addition of stalactites and stalagmites peppering the caves and various plants growing in the darkness.
There’s a host of new mushrooms that can be made into stews and some even emit light.
You’ll also notice several new stone blocks that can be crafted into new bricks and stairs.
And to make the new underground even more exciting is randomly generated structures. These are similar to finding dungeons as some may have mob spawners in them but a lot are more reminiscent to ruins. They also likely contain treasure pots with random, useful items inside.