Heart of Darkness is a mod for registered Wolfenstein, made by Ross Williams. Released as a test demo on June 16, 2003, it was only available on Williams' own site and never uploaded on the Wolfenstein 3D Dome though it was mentioned in a news post.
A handful of test levels were featured, and as per the title screen, Williams also tried a hand in coding this project; hitherto his only projects had featured new maps and graphics.
Envisioned as a TC, Williams gave a release date of July 4, 2003 but this never came to be.
The mod is currently unavailable and is sought after.