The original Playstation is where From Software got their start with the well-regarded-but-definitely-niche King's Field series of first-person dungeon crawling RPGs, and Shadow Tower was the last game they made in that vein for the PS1.
Released in 1998 in Japan, and then a year later in the US in 1999, Shadow Tower met with poor critical reception. It was fully real-time 3D rendered and much better looking than the King's Field games but was an unforgiving survival horror/hardcore dungeon crawl released near the end of the PS1 lifecycle, which resulted in the game selling extremely poorly and being nearly forgotten.
Interestingly, a number of the design decisions that would meet critical acclaim a few decades later when From re-imagined the King's Field/Shadow Tower games into the wildly popular Souls series appear in this game, nearly fully formed.
The game is set on the continent of Eclipse, in the Holy Land of Zeptar. The player takes the role of a mercenary named Ruus Hardy. Returning home to Zeptar, he finds that the entire city, as well as the central tower, have been sucked into the underworld. He meets an old man who gives him the Dark One's sword, the only weapon which can injure the demons responsible. Swearing to rescue the old woman who raised him, as well as the rest of Zeptar, Ruus descends into the underworld.
The majority of the game's narrative is found in a short synopsis in the manual, with a handful of additional snippets revealed (in true From Software fashion) via item descriptions and a small number of NPCs who run the gamut from actively hostile to slightly helpful.
The game (in)famously has no soundtrack or music - the audio consists entirely of ambient sounds and dynamic noises from denizens of the Shadow Tower.
The game is notable for having a fixed amount of items in the world, as well as a fixed amount of currency and a fixed number of monsters that do not respawn - anything that is killed or picked up stays killed or picked up, meaning a player can "clear" the entire game if they wish (indeed, the game tracks this as a stat) - these mechanics favor a methodical approach, as even if an area is populated with many powerful enemies, every single enemy killed makes the game permanently easier.
Additionally, the game features weapon and armor degradation, but with the unusually cruel twist that the degradation can only be repaired by spending the player's health points, which can only be replenished with uncommon health potions, of which there are a finite number in the game.