Randomized Stone Structures

This idea focuses most of all on the Wow!-factor of structures that the player finds for the first time. World Generation is mostly randomized, so this would probably not be too hard to implement and also not a major or drastic change to the game. 

Now, the idea is quite simple: Add randomly generated stone structures to the surface of our beloved overworld. These could be everything from 1 block to about 50 blocks in height and about the same with the width. They'd often be oriented to either be tall and not that wide or flat, covering a rather large area of about 30 times 30 blocks. All kinds of naturally spawning stone (that doesn't only appear in other structures, so no bricks) could be included, with normal stone being the most likely to generate and the others having a significantly smaller chance of appearing. They could be just one solid piece of stone but also a field full of scattered rocks. Almost all non-water-themed biomes could have them generate inside. In normal biomes they would be covered in a 1-block layer of grass, in ice biomes they'd have an icy or snowy (or even snowier) top and in stone-themed biomes they wouldn't have a topping at all. In deserts, they would be made out of sandstone. There would be a tiny chance for ores to spawn in these structures.

Example pictures: