The Nether

As usual, access to the Nether is via a Nether Portal. Thus, the gating factors are Obsidian and an ignition source. However, prior to visiting the Nether, the player will not have access to Flint and may not have access to a Diamond pickaxe. Working with what is available, the ingredients are instead: Water, Lava, and flammable blocks... The process is likely familiar to anybody who speed-runs Minecraft, but less so to other players.

Construct the Frame

(If the player has at least ten Obsidian, this step can be replaced by merely constructing the portal frame with it...)

The player must create a space to construct the portal where the floor is fireproof. After that, a curtain of falling water should be created behind or in front of the desired portal frame (run solid blocks above the level of the top of the frame to-be and dump buckets of water on them). Next, the player works their way around the frame, placing lava in the open spaces adjacent to the water where obsidian is desired. The lava will immediately convert to obsidian.

Ignite the Portal

If the player has not already done so, next the water should be removed. The player must place flammable blocks (such as planks or leaves) next to the frame (but not inside of it). Finally, lava must be placed next to or among the flammable blocks. Bear in mind the flammable blocks will be consumed and thus cannot be counted on to contain the lava. The lava should ignite the flammable blocks. Continue adding more flammable blocks if necessary until the flames spread to the inside of the frame, which will immediately ignite the portal.