Elemental Lock

"Knick Knacks and Other Oddities. Sure, we can take a look."
The two friends wandered into the small store. A wizened old man sat unmoving at the back of the store.
"Knick knacks and junk, I'd say! Check out this rusty old lock!"

This lock looks crude, as if even the most amateur of thieves could open it. The key is a very simple, old-fashioned key. But once it is locked, it is nearly impossible to open without the key. In fact, it is nigh impossible to cut through or otherwise destroy the lock.
It works by housing an entrapped elemental, which keeps the lock closed. Only the key (which has a shard of the elemental) can open it. Or very strong magic. The same elemental prevents damage to the lock, even providing a bit of resistance for whatever the lock is on, if it is metallic.

Item type

Magical