The cheapest portal frame

A portal needs a frame at least 4 wide and 5 tall, with a 2x3 opening inside. The corners are optional, so you only need 10 obsidian. Light it with flint and steel or a fire charge.

Link portals exactly

One block in the Nether equals 8 blocks in the Overworld. Divide your Overworld X and Z by 8, then build the Nether portal at those coordinates. The Y level does not need to match.

Build a Nether highway

1. 1
   Tunnel at Y 15 or near the roof

   Lower levels have fewer ghasts and more safe netherrack walls.

2. 2
   Make it two blocks tall

   Use blocks ghasts cannot blow up, like cobblestone.

3. 3
   Add ice for speed

   Blue ice with a boat is the fastest way to travel in survival.

4. 4
   Mark every exit

   Put a sign at each portal with the Overworld location it leads to.