How do you get A Terrible Fortress in Minecraft?

Enter the Nether through a lit portal, geared up: iron armor or better, a bow, food and a stack of blocks for bridging over lava.

What kind of advancement is A Terrible Fortress?

A Terrible Fortress is a Nether tab advancement in Java Edition.

A Terrible Fortress

Tab: NetherDifficulty: Medium

Quick answer: Break your way into a Nether Fortress

Previous advancement: Nether

How to get A Terrible Fortress

Enter the Nether through a lit portal, geared up: iron armor or better, a bow, food and a stack of blocks for bridging over lava.
Explore until you spot the dark red nether brick structure. Fortresses can generate in every Nether biome: the game splits the Nether into 432x432-block regions (480x480 in Bedrock) and each region rolls either one fortress or one bastion remnant, never both.
If a region gave you a bastion instead, keep moving: in Java each region has a 40% chance of a fortress (33% in Bedrock). In basalt deltas any structure attempt becomes a fortress, so fortresses are most common there.
Walk into the fortress itself. Just stepping inside completes the advancement.

Tips

Fortresses can generate buried in netherrack with only a bridge or a tower sticking out, so scan the terrain edges. Don't confuse them with bastions: bastions are black blackstone, fortresses are dark red nether brick. A fire resistance potion makes the search far safer.

More guides from this tab (Nether): Return to Sender Those Were the Days Hidden in the Depths Subspace Bubble Who is Cutting Onions?Oh Shiny