Expanded Caves

Underground terrain gains a range of new blocks built from the stone types, plant life and structures that the mod generates in caves. The content follows vanilla-style terrain so it blends with existing caves, and most of it can be disabled or adjusted in the config file, which is commented for editing. Builds exist for Fabric and Forge, and the mod runs on client and server, so both the server and every player need it.

The 1.16 line is the mature version, with Expanded Caves 2.4 worlds loading in the 1.16 build after only a few minor recipe changes. The 1.18 line is still a work in progress and contains most of the 1.16 features, some renamed, while others were modified or removed to work better on 1.18. Its alpha builds are published for 1.18.2, and its latest Fabric file, 4.1.0-fabric for 1.18.2, is an alpha release. Forge builds cover 1.16.5 and 1.18.2 as well, with 3.0.3 for 1.16.5 as the latest Forge file.

The mod is released under the CC0 1.0 Universal license and is open source, with a public source code repository and issue tracker. The developer's notes say the core code was stripped and rewritten to fix a number of bugs and make the mod easier to maintain, and that the broken stone option can be disabled in the config.