Echo Chamber:

Once it's placed down, if there is two or more Echo Chamber in the same dimension, using it will give you a menu that allows you to instantly transport between them, they can also be color coded with a combination of 3 dyes in it's menu, the player can also use commands to make it so that you can ONLY teleport between Echo Chambers of the same color (for the sake of adventure maps and stuff)

The idea of this is to cut back on back tracking over long distances, echo shards make it so you need to explore the ancient city to find them, and since they are non renewable, the player has to be wise about where they use them

Echo Locator:

An item that allows you to access the Echo Chamber network from anywhere, it utilizes durability

(Advancement: "Echoes of the past" use an Echo Chamber)