Lavacast

Overview
Lavacasts are enormous cobblestone structures, frequently used on 2b2t as means of griefing. While they are ridiculously easy to make, using only water and lava, a lavacast exponentially grows in size as it is being made. A lavacast usually comes in the shape of a piramid, made from many layers of cobblestone. They rely on the generation of cobblestone when water and lava collide. Players first let lava flow over the lavacast, and once it reaches the bottom they empty out a water bucket on top, which flows down and turns all of the lava into cobblestone.

Videos
A video showcasing the process of creating a piramid-shaped lavacast:

https://www.youtube.com/watch?v=aKVyufU38pQ

A video showcasing a staircase-shaped lavacast (these are easier and faster to make, helpful for when you have limited time.)

https://www.youtube.com/watch?v=ic66zk_BtDs