Heart of the Golem

Heart of the Golem is an enchanted dagger +2. It can be gained from the area with tomes or it can be gained when you kill Marek.

In-game description
"Dagger +2: 'Heart of the Golem'. There are no records of this weapon creator, nevertheless, its existence can be traced back among thieves and murderers to before Dalereckoning. Its blackened blade was apparently forged from the arcane metals of an iron golem, giving the weapon an appearance as dark as its history."