To prepare for a 1.17 survival world with my friends, I decided to make a quick data pack that added the lush cave features and dripstone cave features to certain biomes. However, I had some extra time on my hands, so I thought to myself, "why not make some new cave features too?"

...I may have gotten slightly carried away.

This data pack adds in new cave biomes to the world generation, as well as the experimental generation features and the upcoming 1.18 cave biomes. Unlike the plans for 1.18, this data pack puts specific cave biomes in specific overworld biomes. The new biomes aim for a vanilla-like feel, so only naturally generating blocks were used for features (with a few exceptions). Below is a list of all the cave biomes and what biomes they generate in:

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Lush Caves
Generates in:
Plains
Sunflower Plains
Flower Forest
Swamp
Swamp Hills

The lush caves are mostly unchanged from their 1.18 counterpart, though the features will not be as common in plains biomes (due to feedback). In the swamp biomes, regular vines will generate more frequently within caves.

Dripstone Caves
Generates in:
Mountains
Wooded Mountains
Mountain Edge*
Gravelly Mountains
Modified Gravelly Mountains

The dripstone caves are mostly unedited from their current preview state, though calcite blobs have also been added to these biomes.

Desert Caves
Generates in:
Desert
Desert Hills
Desert Lakes
Badlands
Eroded Badlands

The desert caves feature sandstone blobs and sandy floors, as well as the odd cactus. Pillars of bone blocks will hang from sandstone ceilings, and larger coal ore veins can generate at any altitude, allowing you to stock up on torches even if you're at the deepslate level. The sand and sandstone will be replaced with their red counterparts under badlands biomes.

Frozen Caves
Generates in:
Snowy Tundra
Snowy Beach
Snowy Mountains
Snowy Taiga
Snowy Taiga Hills
Snowy Tiaga Mountains
Ice Spikes
Frozen Ocean
Deep Frozen Ocean

The frozen caves feature blobs of ice, packed ice and blue ice, as well as snowy floors and ceilings. Small pillars of ice can hang from the ceiling. Large ice blobs can completely expose ore veins or other nearby caves, so it's always good to peer inside them and see what you might find. Just don't get too distracted, or you'll fall in some powder snow.

Shroom Caves
Generates in:
Giant Tree Taiga
Giant Tree Taiga Hills
Giant Spruce Taiga
Giant Spruce Taiga Hills

Underneath giant taiga biomes, podzol and coarse dirt will cover the cave floors, with plenty of mushrooms on top. Giant mushroom stems hang from the ceiling, and some large mushrooms might be found on the floor.

Mycelium Caves
Generates in:
Mushroom Field Shore
Mushroom Field

The mycelium caves are similar to the shroom caves, but with mycelium instead of podzol and coarse dirt. There are plenty more giant mushrooms here, and the water is purple. Who doesn't love purple water?

Ocean Caves
Generates in:
Cold Ocean
Deep Cold Ocean
Ocean
Deep Ocean
Lukewarm Ocean
Deep Lukewarm Ocean
Warm Ocean
Deep Warm Ocean*

Ocean caves are full of prismarine, allowing you to finally build nice ocean structures without having to make guardian farms. Sea lanterns sometimes hang from the ceiling, lighting up the surrounding parts of the cave. The ocean caves do have a lot more flowing water though (especially in the deep variants!), so they might be a bit more annoying to navigate. In lukewarm oceans, a few patches of coral will generate, but they'll generate much more frequently in warm oceans. These coral patches can contain sea pickles, which adds even more light to the caves, making these caves quite a sight to behold, even without night vision.

Roofed Caves
Generates in:
Dark Forest
Dark Forest Hills

The tops of roofed caves are covered in dark oak leaves, and the floor has patches of grass and coarse dirt. Dark oak trees will generate on top of the grass patches, creating dense forests even within pitch-black caves. How do trees grow in the dark, you ask? Well uh... um...

Hot Spring Caves
Generates in:
Jungle
Jungle Edge
Modified Jungle
Modified Jungle Edge

On the floor of these caves, ancient volcanic activity has created hot springs with melons growing in them. Some patches of grass are also found, with jungle trees somehow growing up despite the lack of sunlight. Similarly to the roofed caves, a leaf canopy generates across the cave ceiling.

Terracotta Caves
Generates in:
Badlands Plateau
Wooded Badlands Plateau
Modified Badlands Plateau
Modified Wooded Badlands Plateau

The terracotta caves feature lots of, well, terracotta. Similarly to the badlands biomes above, the colour of the terracotta will change depending on the height level, though you can also find plenty of uncoloured terracotta in blobs. If you're really, really lucky, you might strike gold in these caves, so keep digging!

*The Mountain Edge and Deep Warm Ocean Biomes do not generate in vanilla worlds, but they will generate their respective cave features in a single biome world.

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Installing the Data Pack
To install this data pack, simply add the zip file to the data packs folder when creating a new world. Because this data pack edits world generation and world height, you cannot use this data pack on existing worlds. This data pack is not compatible with any other pack that edits overworld generation, but it should work with data packs that only edit other dimensions. This data pack includes all of the caves and cliffs preview pack features, so you do not need to use that pack if you're using this one.

The datapack was last tested in 1.17.

I hope you have fun with this pack. If you have any suggestions or feedback, feel free to comment; I might update this in the future if people are interested.