From Populous Wiki

Three types of Discovery usage on PopEdit: two are under vault and stone head, and one alone

Discoveries are what allows the tribes to get rewards. They have three types:

  • once - you get one shot of whatever is on the discovery
  • level - you permanently get whatever is on the discovery
  • permanent - you permanently get whatever is on the discovery

Then, the discovery states the reward:

  • Building - any Populous building
  • Spell - any Populous spell (except for Ghost Army)
  • Mana - the amount of mana your shaman will be rewarded with
The outcome: You see rewards in vault and standalone discovery, but not on the stone head

As both pictures tell us, discoveries are usually placed under stone head / Vault of Knowledge. When placed alone, they are usually not linked to a trigger, and any tribe unit or diety can just approach the location and click on it to get the reward (see img.2 invisibility).

Rewards are visible on both standalone and Vault of Knowledge discoveries, but not on stone head / Totem Pole / gargoyle / obelisk.