Hardcore Spelunking

Tired of players simply digging straight down to bedrock and strip-mining ores, completely ignoring the thrilling challenge of wandering alone through hostile caves and dangerous ravines? Then this mod will make your players love you!
How the modification works
The mod intervenes in the world generation process right before it completes. If a stone block is more than three blocks away from a cave or air, it gets replaced with solid bedrock. This means you'll have to use cave systems to find ores and bravely descend into the dark depths. Don't forget to stock up on torches to light your way. Helpful tip: place torches on the right wall while exploring, then when returning back you can navigate by keeping the torches on your left.
Gameplay features
However, this mechanic has a downside - underground bases become less practical, and if there's a hill near your house that you don't like, you'll have to accept its presence.
Configuration
If you find that there aren't enough cave systems going deep enough, you can increase the number of generated caves and ravines in the .cfg configuration file.
Technical details
Since world generation happens only on the server side, this mod needs to be installed exclusively on the server. Players without the mod will be able to connect and play without any issues.