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 is known of Slaughtergarde or Mu-Tahn Laa at this point.