The Minecraft Caves & Cliffs update is expected to hit in early 2021, but ahead of that milestone Mojang has issued the first snapshot showcasing its new content. Snapshots in Minecraft are basically testing phases which can be accessed only in the Java edition.
The snapshot doesn't appear to affect cave generation, nor does it feature the new Lush and Dripstone biomes. But there's plenty of new stuff to see and experiment with, and arguably the most exciting of these is the new Amethyst blocks. Not only do they look really pretty (that's them in the picture above) but they also make "beautiful sounds" when they're interacted with. Expect some clever music making from some of Minecraft's most dedicated players.
Also in the snapshot are bundles, which according to Mojang are "items that hold other items". Elsewhere, there are candles that come in 16 different colors, cauldrons that can be filled with lava,a spyglass for gazing into the landscape, and tinted glass.
Snapshot 20W45A is a pretty generous slice on new content, and in addition to all the new material there are also changes to existing stuff. For example, minecarts work under water now (hooray) which means, naturally, that railways do too.
The full, lengthy rundown of the snapshot can be found over here, and again, you'll need the Minecraft Java Edition to gain access to it. For everything else you need to know about the Caves & Cliffs update, look no further.