Sädekivi

The Beamstone (in-game name Sädekivi), is an inventory item. It can be obtained by collecting the Summon Sädekivi perk.

Usage
If you kick the item while it's on the ground (or try pulling it with Telekinetic Kick perk), it will vanish, and a beam of light will appear in its place. Along with it, a message:

This beam will charge up for a few seconds, before exploding, dealing 375 damage to any creature unfortunate enough to be inside. Additionally, all solids above the beam, even unloaded ones, will be removed in a wavy pattern.

It makes for a great tool to get back to the surface.