The Old Ironforge is a huge cave inside/under Ironforge. Old Ironforge is also known as Hall of Thanes or the Assembly of Thanes
The Hall of Thanes is a massive, natural cavern complex. It is located in Ironforge’s lowest depths. The area is a true marvel of organic stone formation: no dwarf has touched this area with pick or chisel. Ironforge’s kings are buried in the Hall of Thanes, and the old throne is here as well. Also within this cavernous area is the ancient, weathered Iron Forge — perhaps the greatest titan artifact ever unearthed. The dwarves do not use this holy anvil, but keep it near their honored dead and the seat of their power. Brann Bronzebeard believes that as dwarves uncover more truths about their ancestry, they will find greater uses for the Iron Forge. He believes the titans must have given it to them for a reason.