Man, Sega really was all over the place back in the mid-'90s. It produced a capable console in the form of the Saturn and pumped out some amazing ports of its arcade smash hits, but then it also parcelled off valuable resources to produce critical and commercial duds like 1996's Congo: The Movie: The Lost City of Zinj.
Following on from the events of 1995's now-largely-forgotten Michael Crichton-inspired Congo, this equally obscure FPS was developed by Jumpin' Jack Software and published by Sega itself, making it a rare console exclusive for Saturn.
Hardly any outlets bothered to review it, and those that did weren't impressed. It's easy to see, then, why the game's suite of cheat codes has gone undocumented until now, almost 30 years later. The codes have been discovered by @memory_fallen, who has a talent for unearthing secrets in decades-old video games.
As well as the unlimited health cheat noted above, some more codes have been discovered, including one for unlimited ammo, a level skip and a level select.