Obsidian Crate

The Obsidian Crate is a pre-Hardmode crate that can only be fished in lava. Opening Obsidian and Hellstone Crates crates is the only way to obtain the Obsidian Lock Box, and therefore any Underworld-exclusive items normally found in locked Shadow Chests, once the Underworld has been fully looted. Its Hardmode counterpart is the Hellstone Crate.

History
Caisse d'obsidienne