Thief: The Dark Project (Steam)

Thief is a first-person stealth game that likes the dark. You sneak through the ruins of haunted cathedrals, subterranean ruins, and forbidding prisons, in a dark and sinister city - heavily inspired by Steampunk and the Dark Ages. Garrett finds an ally in the shadows, as he steals for money and uncovers the hidden agendas of allies and enemies. The story that unravels is one of deception and revenge.