Morrowind:Savant

Savants are people who possess a wide variety of knowledge on many diverse topics.  In their own words:

:I am a savant. I am a man/woman of wide learning and cosmopolitan tastes, a well-traveled man/woman, educated, refined in manner, able to converse on various topics with authority, and a man/woman ever ready to defend his/her honor, and the honor of my companions. In short, you see before you a gentleman/gentlewoman. I can discourse upon history, speechcraft, language, and customs. And, for a fee, I offer training that will permit you to share a few of my many virtues.*

  Note that while they all claim to offer training, only about half of them actually do.

During several quests, you may be directed to speak with a Savant in order to obtain more information.  The Dark Elf Savants in particular are among the most knowledgeable.  Among the general information they can provide is:
The locations of every city and town in Vvardenfell, as well as some of the other more major locations.  They will mark them on your map if you ask about them.
Information about all the Regions in Vvardenfell.
Information about all the Provinces in Tamriel.
Information about all the joinable Factions in the game.
Information about all the Skills in the game.
Information about all the Races in the game.
Various other bits of information about Morrowind lore.
Among the more useful of their information is advice on the following topics:
Boots of the Apostle
:''The place-name reference in the Oracle's prophecy is obvious. An ancient Dunmer stronghold called Berandas lies south of the village of Gnisis in the West Gash region. I would also not be surprised to find that the reference to "wings of twilight" designates the guardians of the treasure you seek. Winged twilights are Daedric servants of the Daedra Lord Azura, one of the Anticipations worshiped in the Tribunal Temple.
cure skooma addict
:I have not heard that there is a cure for skooma addiction. The Khajiit themselves say there is no cure, and they should know. But there is a book I have heard of, 'Confessions of a Dunmer Skooma-Eater,' which claims to be a memoir of a Dunmer woman who overcame her addiction to skooma. This book praises skooma, and says that skooma addicts are not necessarily foolish or evil. Dunmer won't carry such a book. Try Vivec, Jobasha's Rare Books, in the Foreign Quarter.
Halls of the Dead
:That might be any Dunmer ancestral tomb. The ancient Dunmer word for ancestral tomb is 'cardruhn'. 'Ruhn' translates as 'home' or 'hearth-hall'. 'Card' means 'undeparted kin-wardens'. The sense is very close to your phrase 'Halls of the Dead'.
Ring of the Wind
:Perhaps I can help you with the Oracle's riddle. Nammu, or 'no-name,' is a cavern in the wildlands of Sunna Guradan. Its east-facing entrance is west-north-west from the Daedric ruin Yansirramus. At the heart of the cavern is a great high chamber, flooded, with a central spire rising from the water. The water around the bottom of the spire might be the ring of water in darkness from the Oracle's vision.''
Some Savants also offer services - generally buying and selling a small selection of Books and offering training, generally in Mercantile, Speechcraft, and either Athletics or Short Blade.

Bugs
 
  You can enter the console command   to exit the loop.

See Also
Savants' Notes on Vvardenfell – An essay written using only in-game dialogues of savants

List of Savants