Triple Underground Ravine (Bedrock 1.17)
Minecraft Seed: 1239074858
This seed spawns you in a large forest biome, but if you travel in the right direction you might find a good sized ravine with an amethyst geode inside (coords: 137 88 359)
Next to the amethyst geode is the entrance to a large cave system, and if you explore around a bit you might find an underground ravine. (coords: 66 24 314)
This ravine looks normal at first, until you realize that the corner of another ravine is intersecting with it, which also has yet another ravine cutting through it! Each of these ravines are completely underground, and one of them reaches deepslate level.
I didn’t find any diamonds unfortunately. There’s even yet another amethyst geode nearby (coords: 48 22 343)