1.29 brings improvements underground as well. With devices becoming faster and faster, I can tweak the numbers and make the engine generate more stuff without having 90% of the users complaining about low framerates.
Here come massive magma chambers:
This chamber is huge and more than 20 blocks deep, reaching maybe all the way to the bedrock.
All in all, about 15x as much magma than in 1.28. No longer is it safe to blindly dig ahead.
2x longer caves, with wider corridors and more branchings: