Horror from the Deep/Quick guide

Getting started

 * Head to the Lighthouse North of the Barbarian Outpost and talk to Larrissa.

Reparations

 * Go South to the Barbarian Outpost and enter the agility course.
 * Talk to Gunnjorn.
 * Use Planks and sixty Steel nails on both sides of the bridge East of Larrissa.
 * Talk to Larrissa.
 * Search the bookcase on the first floor of the lighthouse.
 * Read the Manual and Ancient diary.
 * Go to the second floor and use Molten glass, Swamp tar, and a Tinderbox on the lighting mechanism.
 * Talk to Larrissa.

The Battle

 * Go to the lighthouse basement.
 * On the strange wall, use a Fire rune, Air rune, Water rune, Earth rune, a Sword, and an Arrow.
 * Go down the ladder and kill the Dagannoth mother.
 * Strategies can be found here.
 * The following table shows her weaknesses in different forms:
 * Quest complete!