Seaview Keep was built hundreds of years ago on the western edge of the Duchy of Uldus by an ambitious nobleman from the Empire of Toutus. He had been sent to pacify the human tribes and demihuman clans of the Teiglin Peninsula & bring them under Toutian influence. It was built to hold a substantial garrison and enough stores for the garrison to survive at least a month under siege.
During his final years, the nobleman took on Zelchus, a wizard of some renown, as the mage-in-residence. When the nobleman died without an heir, Zelchus took over the keep without delay, expelling those who protested and bringing in his own allies. However, he also met Toutian Imperial officials and promised to toe the Imperial line and to fight against the foes of Toutus.
The Imperial officials agred, so long as Zelchus relinquished any claims over the nascent province of Teiglin. He agreed, reluctantly. Although on the boundary between the duchies of Uldus and Teiglin, Seaview Keep was placed under the lordship of Teiglin.
Zelchus kept the above-surface areas of the castle working as normal. Down below he initiated construction of a large dungeon network of no less than three main levels and numerous sub-levels where he kept his laboratories, enslaved monsters, cunning traps and animated undead troops. He also took on four apprentices who assisted him in his strange work.
When Zelchus died one apprentice simply left of her own accord, another died of poisoning while working with alchemical substances (accident or foul play?) and the other two gathered their respective forces and did battle for the control of the dungeons, using summoned and charmed monsters, traps and hired mercenaries (both human and otherwise). Many humans fled from the surface buildings as monsters sometimes erupted from beneath the keep. After several months of fighting the two apprentices were killed by each other's monstrous troops on the same day.
Human troops from Erkhart came and retook the surface buildings and a Toutian wizard used a wizard-lock spell on the trap door leading into the dungeons. During the Wars between the Empires the surface garrison saw action against Bursian raiders on several occasions but survived. However, it could not withstand the horde of chaotic monsters that attacked when Bhael created the Chaos Portal in Erkhart. Someone or something has undone the Wizard-lock spell and the chaotic creatures from the portal are mixing and sometimes fighting with the creatures that remain from the apprentices' battle all those years ago.
Normal, sane folk would not ever wish to go near Seaview Keep as it is today. It is on the wrong side of Teiglin, looking out over the Godsblood Straits. It is isolated from civilisation, infested with monsters from both inside the dungeons and from outside. There are rumoured to be a number of deadly traps to slay unwary intruders.
However, there are great rewards for the intrepid and capable. The original nobleman and the dark magic user Zelchus were both very wealthy and brought in considerable amounts of silver and gold. In addition, Zelchus was an avid collector of magic, including spellbooks, magic weapons and miscellaneous trinkets of power, while at least one of his students was adept at creating magical potions.
Seaview Keep is large on the surface (most of the walls and towers and some of the outbuildings are intact), and vast once underground. It has been suggested that it is impossible to actually clear out the dungeons of Seaview Keep, but is best explored in short, sharp expeditions with particular goals or limits in mind.