The Crimson Sea is the red sea that surrounds the whole continent of Tayira. Its waters are poisonous, and drinking a mouthful of it will cause certain death. They also release a poisonous mist, which at their strongest, when inhaled for more than a few minutes will cause a creature to go unconscious and, eventually, die.
Around twice every month, the Crimson Mists, as they are called, extend beyond the waters of the sea and envelop the whole continent, in an event that can last a a few hours. To survive outside, people use the Cleansing Masks (also known as Stoff) which are able to filter the toxic fumes and enable regular breathing.
The mists react to magic, and magic can be used to shield regions and people from it. Experienced arcanists can even harness this power to fuel spells. However, some people - such as most citizens of Erberos - believe that arcane magic is the cause of the mists.
For these reasons, no one in Tayira has ever successfully ventured outside of the continent, with few even believing there would be something to find.