The Ruined Castle first appeared in the Child's Play livestream Shadow of Israphel special. The team went back in time with Simon playing Verigan Antioch and Lewis playing Karpath Antioch to show the events that led to the Shadow of Israphel series. In Isabel Peculier's Tale, Knight Peculier can be seen exploring the ruins, possibly looking clues about Israphel, or his father.
Little is know about the ruins but they are clearly very old as they were ruins even back when Professor Grizwold was adventuring. The team camped out for the night in a ruined ship docked at the castle.
It turns out from the museum server that the ruins are actually located on the same map as the rest of Shadow of Israphel, some distance east of Verigan's Hold and can be accessed by following the Wall. This may not be its original location however and may only have been put there for the sake of the museum. Although the Wall was not there on the livestream this makes sense as the events in the livestream would have occurred many years before the erection of the Wall.
There can also be found a Hellgate just east of the ruins and may have something to do with the reason for them being ruins, however, this is odd as Professor Grizwold said he had only activated one portal and that was inside the castle. Note that beacons of fire activated when he activated the Hellgate, and it's possible those are the same ones on the Wall, which also explains why following the Wall leads to the ruins.
Underneath the Ruined Castle there is a huge soul sand volcano and a dragon made of netherrack with fire along it's spine, possibly a decoration piece or a base for the Cult of Israphel.