Tears of the Kingdom’s Depths — the underworld beneath Hyrule’s surface — is the game’s most content-dense optional area. Accessed through chasms scattered across the overworld, the Depths are lightless, filled with Gloom that drains hearts permanently until cooked Sundelion meals are consumed, and mapped entirely separately from the surface world.
The Depths contain Lightroots at positions that mirror Shrines on the surface — discovering a Shrine unlocks an icon that shows where its corresponding Lightroot is located below. Completing the Depths requires either knowing this mirror system or treating it as independent exploration, which takes significantly longer.
Hidden in the Depths: Bargainer Statues, a secondary currency exchange system using Poe spirits collected only in the Depths. The rewards include armor sets and items not available through any other progression path. Several of these are endgame-quality equipment hidden behind a currency system that requires significant Depths exploration to accumulate.
The most significant Depths secret: at specific map coordinates directly below Hyrule Castle, a chamber in the Depths contains a complete mural depicting the events of the Age of Calamity. The mural is interactive — examining different sections produces lore text that fills in backstory not covered by any surface quest. It is the most information-dense lore delivery in the game, placed at a location only discoverable by treating the Depths as a primary exploration goal.
The detail work the devs put into areas most players never visit is what separates great games from good ones.
I’ve put 200 hours into this game and never caught this. The developers really reward the obsessive players.