Ultima VI: The False Prophet/The Underworld

The gargoyle city of Investigation
The Healer will restore health to any character for free. He may make mistakes: just insist, and he will eventually heal your party properly.

After talking to the Goodscrafter or the Weaponsmith, you can take any item in their shop for free. The Weaponsmith also talks about the Snakecharmer, who lives far away in the south-west. If you blow the silver horn, several silver serpents will appear: they are powerful opponents, but they are a good source of experience points.

Talk to the Foodmaker, and he will give you some nutritious horse meat. It sounds weird, but apparently the Avatar and the Companions never ate horse meat before. The reason is unexplained: this is possibly an open thread in Ultima 6.

The Healer, the Foodmaker and the Weaponsmith all blame the Goodscrafer's negative attitude. Farmer Krill criticizes Farmer Nash.

Finally, several mute, wingless gargoyles walk the streets of Investigation.

The tomb of kings
This is an optional dungeon. No character says anything about it.

This dungeon is a great place to let Beh Lem gain experience quickly. Each silver serpent defeated is worth 91 experience points.

The tomb of kings can be subdivided into four quadrants, each one with four crypts and one lever rooms. Cast "Magic Unlock" and enter the lever rooms, defeat the silver serpent there, then activate the levers to open four portcullises. One of the sixteen portcullises will not open: Sherry the mouse can enter there (and get a single black pearl and another boomerang. The tomb at the north end is blocked by an electrical field; there are six switches in the eastmost and westmost tombs: you need to operate just one to deactivate the electric field.

The human lens
Navigate Dungeon Hythloth all the way back to the human world. Naxatilor asked you to bring a concave human lens. Ephemerides is a scholar in the Lycaeum who makes lenses and sextans. He will ask a glass sword in return for his services.

You can buy a glass sword from Dale in Minoc, but you have to pay him with 10 magic gems instead of gold coins. Nevertheless, you can buy gems in the guild shops: one is in Britain, the second one in Buccaneer's Den.