This creates portal blocks inside the frame, resembling a vortex. Once a frame is constructed, it is activated by fire placed inside the frame.
A nether portal cannot be built horizontally like an end portal.
Adjacent portals can share obsidian blocks. by placing mined obsidian, by completing a ruined portal, or by casting it in place using lava and water. The obsidian can be placed in any manner, e.g. The four corners of the frame are not required, but portals created by the game always include them, resulting in 4 free/extra obsidian.
