Minecraft wiki entry for Things_not_to_do, associated text: If the player builds a nether portal at levels near bedrock, they have a good chance of spawning on a small island near the lava ocean, meaning that shelter area may be limited to only a few blocks of space. Lava oceans usually leave a lot of room which can also hide ghasts trying to snipe the player from the lava. This area does leave the player vulnerable to the possibilities of death or entrapment, depending on whether the fireballs hit the player or the portal. It is recommended that players build their portals above Y-Level 20. Any expedition to the Nether should be taken with caution. Even worse, the player may spawn inside a nether cave, in which the player must dig their way out which is dangerous due to the chance of digging into lava pockets or lakes, or the player can spawn right above a lava ocean, meaning that when the player leaves the portal the player falls right into the lava and die. The player can also spawn inside a lava ocean, and if this happens, the lava destroys the nether portal and the player dies.