Source: Critical Role - Call of the Netherdeep

Wondrous item, rare

This clay tablet is eight inches long, four inches wide, and half an inch thick. Inscribed on it is the sigil sequence for a permanent teleportation circle. A creature that studies the sequence for 10 minutes can make a DC 21 Intelligence (Arcana) check, learning the circle’s destination on a success.

You can use an action to break the tablet in half, turning it to dust. If the tablet is broken while it is on the same plane of existence as the teleportation circle whose sigil sequence was engraved on it, a 10-foot-diameter teleportation circle of glowing blue light appears on the ground in an unoccupied space you choose within 30 feet of you. This teleportation circle has the characteristics of one created using the Teleportation Circle spell, except that it connects to the teleportation circle whose sigil sequence appears on the tablet.

The teleportation circle created by the tablet disappears at the end of your next turn.