Heroes III seer's huts
Heroes IV quest huts
Heroes V seer's hut
The seer's hut is an adventure map structure in Heroes III, Heroes IV, and Heroes V, though in Heroes IV, it's referred to as the quest hut instead. Like the quest guard, the seer's hut will reward the hero for completing a quest, but the seer's hut usually won't open a path.
The reward for completing the seer's hut's quest can take many forms: extra resources, artifacts, extra creatures, a bonus to primary skills, secondary skills, and so on.
Seeking out seer's huts is often a good idea in scenarios, as the rewards are often either necessary or useful for completing the scenario objectives.