Sublevel 1:

After descending down the stairs you will enter into a large cavern (Sub level 1). Inside this cavern are 78 Dagannoth with their spawn and fledglings. They use melee attacks and hit high and accurately. Protect from Melee is highly recommended for players who wish to train here. There are also a few rock crabs to the north part of the area.

Most of the potential safespots have eggs. These eggs when approached will hatch "Dagannoth spawn" that will attack. Once the Dagannoth become non-aggressive, they can be safely ranged across the skeleton just northeast of the entry stairs.

There are areas from the wall directly south of the small obelisk in the East where, if you are not being attacked, none of the creatures will attack you and you can stand there and heal. From these spots you are able to attack them.

Depending on the path taken different monsters will be encountered.

Northern path – Giant rock crabs (level 95)
Middle path – magic-using Wallasalkis (level 91)
Southern path – ranging Dagannoths (level 78)

Door to the central room:

all of the different paths will lead to the "Central Room" with a ladder. This is blocked by 3 door-supports. these can be taken down with any type of attack style. Once the props have been removed 2 "Dagannoth spawns" will hatch and attack. It is also possible that monsters from the 3 paths may also attack as well.

Once the player is in the central room, they can climb the ladder. Going down the ladder allow the player to go through the sublevels that lead to the Dagannoth Kings; going up the ladder will lead to Askeladden, who is on top of the snow-covered mountain in the east part of the island. The top part of the area is very useful for resting, espically when players are going to the Dagannoth Kings.

Sublevels 2-5:

Rooms within these sublevels may have the following:

Wallasalkis, which use magic. Protect from Magic is highly recommended.

Two types of Dagannoth: melee and ranged. If the player plans to run through the room, Protect from Ranged is recommended because the melee Dagannoth cannot run. Otherwise, the player should use Protect from Melee because the melee Dagannoth can actually follow the player, and they are potentially more dangerous than the ranging ones.

Giant rock crabs, initially disguised as large stones. Upon entering the room, the player will be safe providing that the player stays where they are. However, if the player goes near a crab, it will attack. Players may want to go near the Giant rock crabs currently moving, as those will be non-aggressive.

Rock lobsters, monsters similar to Giant rock crabs in that they are also disguised as large rocks. Protect from Melee is recommended.

At the dead end is the location of "Bardur", fighting the Dagannoth Fledglings. If the player gives him certain equipment to keep him going, he will hand the player a cooked shark in return, which may prove a bit helpful if the player wishes to explore the dungeon further.

The largest room in Sublevel 5 starts out as a long corridor that extends east, south-west, and then opens up to a big room with the ladder that leads to the Dagannoth Kings. The first section of this room contains approximately ten level 142 Rock lobsters. Protect from Melee is a must when going past this section of the room; the lobsters hit nearly as fast as dual-wielded darts and often into the low 300s. With multiple lobsters attacking the player, one mistake can quickly prove to be fatal. If players go past the ladder to the Dagannoth Kings, the final room on Sublevel 5 contains the exit to the Lighthouse. Players must complete Horror from the Deep to use the ladder, which will send them into the dungeon under the Lighthouse.

Sublevel 6:

Players that venture up the ladder will appear in a arena where the three kings are located. Each of these kings use a different style of combat. Players MUST be prepared before going down the ladder, or they may die a quick death.

Southern Cave:

During Blood Runs Deep, players gain access to a dungeon near the southern end of Waterbirth Island. It is the home of the Dagannoth Mother, two Dagannoth Sentinels, and many Dagannoth guardians. After the quest, only the guardians remain, since the player trapped the Mother and killed the Sentinels during the quest.