Shrines are a mapping mechanic that can appear inside explorable maps.
According to the main patch notes, shrines can spawn by default in explorable maps, spawn a pack of enemies around themselves, and can be right-clicked to grant a temporary buff.
The original patch notes use the name Hardiness, while extracted shrine item and projectile names use Defense.
Extracted item data also shows biome-specific shrine variants for at least Forest and Desert, which suggests shrine visuals or placements can differ by map theme.
These mapping shrines are separate from decorative structures such as the Glade Shrine shown on the Forest Map page. The Glade Shrine is a point of interest, while the shrine mechanic described here is a combat-and-buff system.