Minecraft wiki entry for Nether_portals, associated text: It is possible to end up in a situation where a Nether portal "randomly" places the player in 1 of 2 possible Overworld destination portals. This is simply because the Nether portal has two effective coordinates as it is 2 blocks wide, say (X, Y, Z) on the left, and (X+1, Y, Z) on the right. If the player entered on the left side, (X, Y, Z) translates to (X*8, Y, Z*8) in the overworld and the game picks the portal closest to that. If the player entered on the right side, (X+1, Y, Z) translates to (X*8+8, Y, Z*8) and the game picks a portal closest to that point instead. This situation occurs when the Nether portal's location is roughly equidistant between the 2 Overworld portals (within 8 blocks overworld distance difference). However, building 2 Nether portals side by side is probably better for destination clarity than building a 2-in-1 portal. It is possible to span distances with pairs of portals in this way, though normally faster to simply walk through the Nether.[1]