The Castle Secrets is a mod for registered Wolfenstein, made by TheSaiyanHog. It was released on June 22, 2009.
Only a 2-level demo, the mod features a number of rudimentary code changes, including new episode names, gun bobbing, increased health and a start ammo count of 10 rather than 8.
A bug is present, as shooting the first guard rewards the player a strangely large amount of points, while killing more guards does not reward the player.
The two levels were rather basic in design. The mod continues with the remaining of original Wolfenstein's Episode 1 levels after finishing level 2.