The Scry command lets you Spy on a distant province. This is more accurate than the automatic Scrying that Arcoscephale has.

Scrying reveals the name, the exact Troop Count, up to three unit varieties (generally the three-most-prevalent), Labs, Temples, Forts, discovered Sites, and the name and type of a random Commander. Stats of the province are also revealed, such as Population. Note that only the Name and Sites will remain revealed after you stop scrying on the province, and that the Sites may also "disappear" after scrying if under Ind's or Ubar's Dominion.

(The hiding might actually be caused by a Dominion change from when you found them; I noticed this only once.)

The Scry command is done at certain Sites, and only by Mages who have a path that matches the site. Scrying in this manner gives you information starting from the turn after you order your Mage to do it, and ending when you have them stop. Exiting and re-entering the Site allows the Mage to Scry on another province, of course. Alternatively, The Thaumaturgy Rituals Scrying Pool and Astral Window let you Scry on a province for potentially longer while allowing your Mage to do other stuff, if you put more Gems into it.