DarkOne-Rob
What has happened already:

 The Abandoned Mine Office and the Whispering Cairn 
 The Three Faces of Evil 
 The Encounter at Blackwall Keep 
 The Hall of Harsh Reflections, Part 1  (disregard action after post # 815  - we will begin at that point, which I have duplicated below the page break.)

 (Current) OoC Thread  (I don't intend to make a new one yet, as there is no need that I can see.    This includes a summary of the action so far! Read it!   )

 

With the party all together again, they can go over their discoveries and review the maps Olofire has purchased. During the lockdown of the Sanctum no one approaches to bother the PCs as they make plans, including the relative of Lyr that is rumored to be looking for Frederick. You are able to rest and recover, either here or at the Crooked House, and begin the next day fully refreshed and ready for business.

When the party begins looking they start in the Artisan's District. Rather close to the map shop where Olofire purchased his new collection they find a business called the "Cold Forge" - an armor and weapon smithy run by a foul-mouther old smith named Crusty Patten. There are numerous ways down into the sewers from the streets, including one out of sight in an alley behind the various businesses.

 
 Spoiler: Mechanics 
This would be easier around a table, but you all managed well enough so I want to get us going...

Finding the next dungeon requires some skill checks. You've already learned a bit about Beggar's Gold, the fungus found on the dead drows' boots. At the discovery of the Cold Forge several of you remember that the fungus often grows in sewers near smithies or forges.

Olofire's efforts have accomplished the "Gather Information" check needed to find the Cold Forge.

Once you enter the sewers you will need to pass five DC 10 Survival checks, keeping an eye out for phosphorescent mold, to find the entrance to the dungeon. As no one in the party is a Ranger or Druid (Lydia has the highest Survival modifier at +4) I went ahead and did the rolls for you.
 

After slipping into the sewers and establishing their light sources and marching orders, the party encounters several minor threats - a wandering gelatinous cube, some darkmantles, and a couple of carrion crawlers - all of which are either dispatched or avoided easily. At one point, early in their exploration, Lydia finds the body of a male human with a large hole in the back of his rotting head. It's a grisly reminder of the threat they face down below the Free City of Greyhawk.

About three hours into the day the PCs find a rather large patch of Beggar's Gold just off an ancient and particularly deep (60 ft underground) sewer tunnel. Here the sewers cross with some natural caves full of the usual stalactites and stalagmites, with a ceiling about twenty feet above. The caves are utterly dark with the exception of the entrance's glowing fungus - there is no light inside except what the PCs bring with them. The natural tunnel walls are unworked stone and the floor is uneven and slippery in most places, making the ground difficult terrain unless otherwise noted.

The first large cavern the PCs find has patches of phosphorescent fungus lighting it. There are huge swaths of the Beggar's Gold fungus and toadstools of various sizes, some the size of a full grown human.

 
 Spoiler: Map 
 
 

 I recommend that the players review carefully the sorts of dangers that can occur underground ( Mundane Environmental Hazards ). We haven't dealt with many of these in a long time (real world), but your PCs would know that such threats exist. Also, there are many, many varieties of interesting (and dangerous) fungus used in old-school style dungeon crawls, especially where Underdark dwellers are concerned. 