The True Lab Is Found

this is the sequel to "If Asriel Never Died", which is exactly what it sounds like, but I won't give too much away for the people that haven't read it, it is my other book on my works
Description of this book (since I was talking about my other book before): It was after the Barrier broke that Frisk and Asriel made the decision to enter the Underground again to retrieve the monsters that had not made it out when they themselves, not including Toriel, Alphys, Undyne, etc. had. It had been going along normal, getting monsters from the Core and Hotland, and bringing them back to their safety at the village the humans had given the monsters. It continued like this for a couple hours until they found an interesting door, or elevator in Alphys lab... is this a secret to the rest of the Underground and the monsters in it? Alphys' is going to have some explaining to do, once they get out of here...