The water dragon's lair is located in a random water-containing square of the wilderness. It contains Shyssiryxius, the water dragon (Blup's mother), her treasure hoard and various other aquatic beasts. It consists of a labyrinth and a central room containing Shyssiryxius and the treasure. The entire cave is submerged, so ordinarily some means of water breathing and the swimming skill are required. The most common method of obtaining water breathing is through a helm of water breathing (generally a "blue helmet" before identification). Wearing two cursed or one blessed rings of the fish also grants this; remember they are autocursing. If the PC is not born with the Swimming skill, it can be obtained from Blup by giving him potions of carrot juice. Swimming is not required but probably increases movement speed underwater. The need for these abilities ordinarily keeps low level PCs out of the lair, which is as it should be. The aquatic beasts found in the labyrinth are not trivial, especially dragon turtles and water elementals. Sharks and giant eels can also be found. None of these monsters see invisible
In theory a PC with on demand teleportation, some regeneration or spenseweeds could survive a teleport to Shyssiryxius, a chat and a teleport to the up stairs without water breathing or Swimming. Drowning damage seems to be dependent on HPs, with high-HP PCs taking proportionally more damage.
There are two main reasons for entering. The first is to 'C'hat with Shyssiryxius then return to Terinyo. This allows the PC to inform Blup about the location of his mother, which results in eventual delivery of the rune-covered trident, a decent artifact weapon and missile, later in the game. The trident is delivered not long after reaching character level 16 for PCs born in the Raven starsign. Others have to wait until level 36. The location of the lair is not decided until the PC starts searching for it, so it is more or less possible to place it in a convenient location, such as near Terinyo.
The second reason for entering the lair is to loot it. There are occasionally outstanding items found in the treasure hoard. As might be expected, Shyssiryxius does not take kindly to thieves and will attack. She does not see in Darkness, however. Cast Darkness over desired item(s), pick them up and leave.
Note that delivery of the rune-covered trident is guaranteed once the PC informs Blup of Shyssiryxius' location. The PC may then proceed to loot the cave, or indeed even kill Shyssiryxius without forfeiting the rune-covered trident.
Monsters tamed in the underwater cave can leave with the PC and breathe air. This is probably a game bug.
2.13.1 Shyssiryxius
Under normal circumstances, Shyssiryxius is not hostile, only intimidating. If she is 'C'hatted with, she roars "HAST YE SEEN MY BABY?" (or "*DIE*" if the PC has done something to make her hostile). Whether she is hostile or not, the PC can leave after chatting and report back to Blup. This of course assumes a PC facing her when she is hostile survives (see below). If the PC attempts to steal from her treasure hoard, she gives a warning about not picking anything up. If the PC persists, she will attack. She is a formidable opponent with a reasonably powerful melee attack and a deadly water breath attack that is capable of dealing circa 400 points of damage in a single round. Sources of water breathing will reduce the damage of this attack. She regenerates and is immune to cold. She is capable of teleporting and does so when she panics, making the PC work to find her while remaining underwater the whole time. She can be killed, but it takes an upper level PC, and it doesn't hurt to have some blessed potions of extra healing along. Note that Shyssiryxius, like certain other powerful monsters, is unable to fight in Darkness unless panicked. She is also vulnerable to poison.