Morrowind:Silent Pilgrimage

Quick Walkthrough
# Talk to Endryn Llethan at the High Fane in the Vivec, Temple Canton for your duties.
# Take a vow of silence and travel to the Sanctus Shrine to perform a silent pilgrimage.
# Activate the shrine to complete the pilgrimage and lift the vow of silence.
# Return to Endryn to complete the quest.

Detailed Walkthrough
Duties
Endryn Llethan at the High Fane in the Vivec, Temple Canton asks you prove your wisdom and patience by performing the pilgrimage to the Sanctus Shrine, west of Dagon Fel. First, you must take a vow of silence and promise not to talk to anyone before you reach the shrine. This means no dialogue with anyone, including bartering, travelling, etc... (though you can deal with the guards if you are charged with a crime); you must make the long trip under your own power. The shrine is on an island west of Dagon Fel and he'll mark it on your map.

Silent Pilgrimage
There is no easy way to travel to the shrine since you cannot speak with anyone, ruling out any form of fast travel. However, you have several options available to you:
Use Mark and Recall - Delay the pilgrimage, travel to the shrine and use Mark. Return to Llethan to accept the pilgrimage and use Recall.
Use Divine and Almsivi Intervention effects to make the journey a little shorter (see Notes).
Donate a Rising Force Potion (any quality, just not a self-made potion) at the Shrine to Stop the Moon outside the High Fane.  This will provide you with a day's worth of Levitation, more than enough to make a bee-line straight for the shrine. You can fly high enough that even the Cliff Racers won't bother you.
Use the Propylon Chambers, provided you have found enough indices to make the cycle around the strongholds. Note that if you have completed the quest from the Master Index plugin, this technique will only get you as far as Caldera. At that point, you must talk to Folms Mirel to go anywhere else, breaking the vow of silence.
Use the Scrolls of Icarian Flight—if you have them—and you could Jump there.

The shrine is outside at the top of the island marked on your map. Activate it to complete the pilgrimage and lift the vow of silence.

Return to Endryn for your reward of four books: Silence, The Four Suitors of Benitah, 36 Lessons of Vivec, Sermon 9 and Sermon 27, which increase your skill in Illusion, Restoration, Blunt Weapon, and Speechcraft, respectively. If you broke the vow of silence by talking with someone but still visited the shrine, you will still receive credit for completing the pilgrimage, but will not receive the books or reputation reward, and Endryn Llethan's disposition will decrease by 5.

Notes
One trivial way to complete this mission is to go to the shrine before starting in, place a Mark right next to the shrine, then fast travel (via intervention and silt strider), start the quest, then Recall.
To make the trip as short as possible using just Intervention spells, use the following directions:
#Walk north through Vivec and exit via the north bridge in the Foreign Quarter.
#Walk north to the first path intersection and cast Divine Intervention. This should take you to Pelagiad, rather than Ebonheart.
#From Pelagiad, immediately cast Almsivi Intervention. You should be taken to Balmora.
#From Balmora, travel north. Walk to the Caldera gates and cast Divine again to be taken to Buckmoth Legion Fort, and cast Almsivi from there to go to Ald'ruhn. Or if you walk all the way through Caldera to the first curve in the road, an Almsivi will take you straight to Ald'ruhn and skip the Fort.
#From Ald'ruhn, head northwest. Go past Bal Isra, and then walk north-northwest until the path goes due-north just past a mud-pot before Manat's Yurt at the Ashlander camp of Mila-Nipal. Cast Divine and you should be taken to Fort Darius in Gnisis.
#From here, you'll have to hoof it the rest of the way, though if you happen to be in possession of the Propylon Indices for Falasmaryon and Valenvaryon, you can just hop down to nearby Berandas and make a few jumps that way.  Alternatively, it helps to have a Levitate or Water Walking spell - you can make the majority of the last leg over water and avoid most hostile encounters.
Inside the shack at the shrine is the book ''Saryoni's Sermons Manuscript'', notable as the most valuable book in the game, and among the most valuable of all items, at 50000 gold. Try not to get caught taking it, or you'll be kicked out of the Temple.
Membership in the temple isn't even required; if you talk to Llirala Sendas to get the "Sanctus Shrine" topic and discuss it with Endryn, he will offer the vow and the quest can be completed in full.
The vow of silence is not broken by talking to creatures such as Rollie the Guar or Creeper. It is also not broken by being accosted by guards for having a bounty on your head, or by talking to the Thieves Guild people who can remove a bounty. There are numerous other cases as well, such as people who will immediately end conversation and attack you. Note that Sleepers will break your vow if they talk to you, so you should avoid doing these two quests at the same time.

Quest Stages