Inspired by Grant Regan's Hidden City over on r/imaginarylandscapes, I decided that I wanted to create something along this theme in Minecraft. Naturally, I would need an immense underground cavern and, since they don't naturally form like that, I knew I'd need to track down a user-created seed.
Five minutes later, I had my seed.
The guys who created it created a superflat world and carved this entire cavern out by hand. It's equidistant to both the surface and bedrock. I'm going to have lots of fun building in hidden tunnels all around the cave walls, ceiling and floor. It's close enough to the cavern in the painting that I can work with it and it is MASSIVE.
Here's a better image of it lit up a little.
I'm predicting this project is going to take me a couple of months (possibly longer since I have a baby due in about six weeks), so check back here for regular updates on the project!