Ruined Portal

A ruined portal is a structure resembling a damaged Nether portal, which generates commonly in both the Nether and the Overworld. It contains some decoration and a loot chest around it.

Ruined portals are the only structures that generate in more than one dimension; they generate in all biomes in both the Nether and the Overworld, except the deep dark. 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.

Ruined portals generate in a grid of squares 25 chunks (400 blocks) wide with 15 chunks (240 blocks) of buffer space between the squares. In other words, a ruined portal can generate at X and Z coordinates between 0 and 399 mod 640. One ruined portal generates per square.