The goddess Auril regards the mythals as an abomination, since the melted her glacier, and so the main goal of the Aurilites has always been to destroy them at all costs. They have almost succeeded a few times, such as in the Battle of the Blizzard.
Each of the mythals is (or was) guarded by a Baelnorn. The presence of the Baelnorns suggests a greater purpose than mere ice cave expansion behind the mythal's existence (but such cannot be revealed on a Wiki at this time).
The known purposes of the mythals are to keep the valley warm, regenerate themselves if one capstone should be damaged, and keep the valley hidden from certain outsiders. The last of these effects is known as the Shroud.
This capstone lies under Beldin Castle. The Thayan Consortium originally had access to the Beldin mythal, but this was ended after the Battle of the Blizzard, with the rebuilding of the city. The Thayans have never forgiven the King for taking away their magical toy.
The name and status of the Baelnorn is unknown.
One of the more difficult mythals to access, the Enclave Mythal's only 'door' is through the Eilistraean Enclave. The Enclave is in turn hidden very well, as a precaution against the Eininfars' many enemies.
The Baelnorn of this mythal has not been heard from in a very long time. The presumption is that Vikii D'Vreeze did something horrible to it.
Kretan's Krawl MythalEdit
This capstone lies as the very bottom of Kretan's Krawl, and is guarded by the shadow dragon Shandowrix. Despite several adventurers' claims of killing the dragon, Shandowrix remains at the bottom of Kretan's Krawl.
Interestingly enough, the one time the Baelnorn of Kretan's Krawl appeared, Shandowrix disappeared.
The Riverfern capstone, like the Enclave mythal, has no physical entry point. The portal to it can be opened by speaking the opening word in the middle of the Temple of Chauntea. The password is 'Flibrasuman', the name of the pet rat of the halfling mage who discovered the entrance. He was an eccentric character.
The Baelnorn of Riverfern is named Galatrin, and she is obsessed with cooking. Sadly she cannot taste anything, but this does not keep her from experiementing with various edible and non-edible substances, and recruiting adventurers into taste-testing for her.
Astrid Deeps MythalEdit
The Astrid Deeps capstone is rumored to be the 'main' mythal, and so valued as the ideal place to carry on any mythal experiments or modifications. It is firmly in the control of the Yuan-Ti of the Astrid Deeps, however.
The existence of a Baelnorn for this mythal is unknown.
The Morraines mythal capstone lies in the old dwarven mines in the Morraines. Unfortunately, it is guarded by fire giants, who have built a settlement around it. The dwarves find this very annoying, but have yet to drive the fire giants out.
The status of the baelnorn is unknown.
This capstone is somewhere in the Lichdoom, though its exact location is rather hard to pinpoint due to the shifting nature of those passages. There is almost certainly something 'wrong' with it, but it has yet to be studied due to the monsters which guard it.
The baelnorn is almost certainly dead--killed by the Demilich of the Lichdoom.