The Merchant Guild contains great treasures, including four random artifacts and a massive number of gold pieces depending on at what level the PC first visits (hundreds of thousands at low levels, millions at high levels). It is possible to access the gold rooms by digging. The bottom-left corner of the right-most room is dig-able, and the top-left corner of the central room is dig-able. The square behind the Great gray wyrm is dig-able, and a corridor of dig-able squares connects the top-left corner of the room behind him to the top-left corner of the left-most room. Unfortunately, the artifacts are surrounded by indestructible walls, and teleportation is prevented on the level until the Great gray wyrm dies.
All monsters in the guild are initially non-hostile. The guild is staffed by numerous gray scribes and is guarded by eternium golems. Chatting with the great gray wyrm while owing money to the merchant guild will cause eternium golems to block the entrance until the debt is paid. Blinding the wyrm will cause him to summon more eternium golems at the entrance every few turns (whenever its "eyes glow deep red").
There are no quests that require visiting the Merchant Guild.