Once you spawn in, head east towards the rising sun and a Savanna biome, you'll hit a body of water, look right and you shall see it. There are a few water falls that go all the way down, which is pretty deep. It goes down to deepslate and beyond the level where diamonds spawn. Its quite massive as well.

Seed: -4911174600997253672

https://imgur.com/a/Bc9YtsL