Eye of the Beholder is a fairly early 3D computer 'role-playing' game. As with all such efforts before about Planescape: Torment, the role-playing aspect is nil, but it's still an excellent game. It's written by SSI and Westwood Associates, and clearly draws on the legacy of FTL software's Dungeon Master. Movement is on a square-by-square basis, and the VGA graphics are quite lush.

The story is set in, or rather under, Waterdeep in the Dungeons and Dragons Forgotten Realms gameworld - by implication, in or around Undermountain. The rules of the game are a surprisingly good imitation of Advanced Dungeons and Dragons Second Edition - although there's a nifty exploit linked to the fact that the designers over-estimated the XP value of kenku. To return to the plot: your PCs have been asked to investigate mysterious goings-on in the sewers beneath Waterdeep. On arrival in the tunnels, however, the group is mysteriously imprisoned by a rock-fall. Only by discovering secret passages and overcoming some slightly implausible monster opponents can you proceed, and discover the secret of Xanathar!

The game was followed by two sequels: Eye of the Beholder II: Legend of Darkmoon and Eye of the Beholder III: Assault on Myth Drannor.

Spoilers ahead!

Level 1: Sewers. Inhabitants: Kobolds and giant leeches.
Level 2: Sewers. Inhabitants: Skeletons and Zombies.
Level 3: Sewers. Inhabitants: Kuo-toa and Flind.
Level 4: Grey stone catacombs. Inhabitants: Giant spiders.
Level 5: Grey stone catacombs. Inhabitants: Dwarves and giant spiders.
Level 6: Grey stone catacombs. Inhabitants: Kenku and one angry mage.
Level 7: Purple stone tunnels. Inhabitants: Drow and skeleton warriors.
Level 8: Purple stone tunnels. Inhabitants: Driders and hellhounds.
Level 9: Purple stone tunnels. Inhabitants: Displacer beasts and rust monsters.
Level 10: Green gungy catacombs. Inhabitants: Thri-kreen.
Level 11: Green gungy catacombs. Inhabitants: Mind flayers and xorn.
Level 12: Grey stone overlaid with mock victoriana in a horrible mauve hue. Inhabitants: Stone golems and the Big Awful. If you haven't guessed the identity of Xanathar, I'm not going to tell you.

There are twelve special quests spread through the game, one per level, and originally there was said to be a prize if you completed all of them and informed SSI. The Amiga version of this game had better cut-scenes than the PC version.

Tips:

To escape the first level, look for two hidden switches, and be prepared to leave something behind.
If at all possible, pick all three locks at the beginning of level two.
On level four, in the room with all the sayings about King Kruen, close the left and right doors, open the middle one and pull the chain. You will receive a powerful magic axe called Drow Slayer.
Keep all stone items - they begin appearing early on. They're portal keys.
Before descending to level seven from level six, ensure that the door into the wide passages, unlocked with a gold key, is open. Failure to do so can result in locking yourself out of about a fifth of the game, including some very useful rooms.
On level nine, in the area beginning 'donate', you can find a +5 long sword, one of the best weapons in the game. Its name is Severious.