Tales of the Bloodstone Lands
According to Pentadrone 1298, the ruins that the goblins found are the remnants of a place called Slaughtergarde, once the fortress of the Demon Lord Mu-Tahn Laa. 186 years ago, Mu-Tahn Laa used a great ritual to bring Slaughtergarde into the material plane in Vaasa. There he was met by armies of celestials and modrons. The demonic host was defeated, but pieces of Slaughtergarde still remain.
1298 called this piece of the complex the Laboratory and asked the party to collapse the entrance after wiping out the goblin intruders.
Nothing else was known of Slaughtergarde or Mu-Tahn Laa at that point.
Later investigations found another piece of Slaughtergarde under the hunting lodge of the Surinak family, demon worshipers from Ostrav in Arcata. The Magnificent Seven discovered drow inhabiting this section of Slaughtergarde, which seemed to house temples and various shrines. They uncovered a trove of scrolls, hundreds of which had barely survived the ages. Tai insisted on bringing these scrolls back to the Wizard’s Guild in Heliogabalus for further study.