Treasures are hidden at locations indicated by the maps. They are unearthed by pressing the action-key whilst standing on the marked spot.
It is not necessary to have the map in order to find the buried treasure if you already know where it is
Locations of the maps and the treasures are:
01 - second floor of ruins (third fight with sir edward)
03 - get this map from nipha, the catgirl whom you first meet in Wintero (post-game)
06 - on right table, inside mount falcon inn
07 - grocery merchant in outpost
08 - secret room in the mansion of the lord, dungeon area.
01 - hunter shield, south of lord darhart's cave, east side of nearest stump.
03 - hunter helm, outside the castle on monster cove, SW of the stairs near the cliff.
06 - ring of curse, ruins of the past, cemetery
07 - mithril armor, near rock wall to the right of the entrance to the cave leading to the pharoah's tomb (or southeast of chest with seed of life)
08 - stun axe, SE of area with the isolated house (bounty hunter's house) in greece.
09 - Boots of Quality, the last area of mt. Falcon, between the tree and the rock.