Minecraft wiki entry for Ruined_Portal, associated text: Ruined portals are the only generated structures that generate in more than one dimension; they generate in all biomes in both the Nether and the Overworld. They can spawn underground, underwater, or exposed to the air. If they generate underground, they have air pockets around them. Natural terrain around ruined portals generates as netherrack. They also generate a mass of netherrack underneath them (including "stalactite"-like shapes, and this may contain blackstone deposits in the Nether). Giant ruined portals have 3 distinct designs, and normal ruined portals have 10 designs. When a ruined portal generates, it has a 5% chance to be a giant ruined portal, for about a 1.67% chance per giant portal design. This gives normal ruined portals a 95% chance, for a 9.5% chance per normal ruined portal design.[more information needed]