You need the Cartographer knowledge from The Archivist in the Unnamed City, then the map room recipe and these materials: 200 Corrupted Stone, 75 Alchemical Base, 50 Crystal, and 35 Iron Reinforcement. The map room is also large, so it usually needs careful placement and enough space to fit properly.

What to gather

  • 200 Corrupted Stone.
  • 75 Alchemical Base.
  • 50 Crystal.
  • 35 Iron Reinforcement.

How to unlock it

You learn the Cartographer knowledge from The Archivist in The Archives at the Unnamed City. After that, you can craft the map room and use it for fast travel once you have attuned to obelisks.

Extra note

The map room is tricky to place because of its size, and one source notes it can fit inside a 7x7 room with 2 walls high.

TL;DR

Unlock Cartographer from The Archivist, then craft the map room with 200 Corrupted Stone, 75 Alchemical Base, 50 Crystal, and 35 Iron Reinforcement.