ycatx's T1/G mission/campaign "Mines of Margroth"
The whole newer series is for Thief 2, but this is the old T1 version of the first mission (never officially released)


The whole series is called "Ruins of Originia"

1 Mines of Margroth is the first mission, also (sub?)titled Bantar's Dungeon
2 Guilded Rivalry
3 Fire and Ice
4 Ashes to Ashes