You've found what you can only assume to be the remains of an ancient structure.
You wonder what it was. A doorway? It looks like it could be a doorway. A really big doorway. Or a… a portal, maybe?
You remember, when you were a kid, watching stories of demons pouring through hellish portals, accompanied by hellfire that crawled over the ground around it.
It'd certainly explain all the lava and weird red stone.
There's a chest on the other side of it. Upon inspection, it contains a collection of golden tools, plenty of flint, and a bit of the material that the maybe-portal seems to be made of. You take them all - and the chest, for good measure.
You leave the mystery ruin be. If this was some kind of hell-portal in its heyday, you don't want to stick around to find out if it still works.
By the time the sun has begun to set, you've made your way into the nearby jungle. You've found some pods of cocoa beans and a patch of melons, which you're more than happy to take. You figure the bamboo you see in the distance will be useful too, but it's getting dark, so you quickly stretch the wool you gathered over some planks of wood, tuck yourself under the canopy, and sleep.
