Nether Portal

The Nether Portal is a player-created or auto-generated structure that allows a player to travel back and forth between the Overworld and The Nether.

Super Minecraft 64 Bloopers: The Nether
It takes SMG4, Starman3 and Mario to the nether. They get trapped in their after SMG4 blows it up. They find a way out by collecting Nether Warts from the Nether Castle, but they end up in Notch's 'raping bathroom'.

SMG4: Mario Preschool
It reappears In Mario Preschool where Steve takes Kids the Nether.

SMG4: If Mario Was in... Minecraft
Mario builds one to get back up to the hole, but gets injured by a Ghast.