To get this quest, teleport to the Heroes' Guild and head to Maze's tower, which is marked by a glowing gold marker. After the cutscene, use any teleporter (including your own Guild Seal) and choose the Witchwood Cullis Gate as your destination. As soon as you arrive in the Witchwood Cullis Gate area the quest will start.
Go straight, hack your way through the vines and keep going, you will come to a corner which triggers a cutscene and introduces a Rock Troll.
Fight them the same way you do an Earth Troll, these guys just have way more health, defence and attack power. This first one will drop two gems. All the rest afterwards will drop one gem or a potion.
Move on through the area to the top right corner of the mini-map, this will take you to the Witchwood Stones.
Nearly right away on your right you will find a Demon Door, talk to him. You'll discover that you need to find out his name before he'll let you in.
Cheat: Just go down to the magic stones and punch out the name HITS (you can also use the letters to spell a profanity for an alternate outcome). A cutscene will trigger, and the Demon Door will open. Go inside to meet the Archaeologist. Look around the cave to find some goodies, then teleport back to the Guild for your next quest.