The Oliver Twins seem to have decided that Mad Carew, the soldier from the poem they're working off, got an elaborate two level chamber as a grave. And there's "A Sharp Diamond" next to it.
Logically, this should be the emerald he acquired and was killed over (the poem does not record the eye being taken back) leaving the diamond to be found in the diamond mine, where the key is or the purse of gold. That would make much more sense.
There's also a stalactite that wants dispatching and what seems to be the counter cog to the portcullis of the castle, nice forward think there. It includes a rope that looks very cutable but, alas, Dizzy has nothing to cut it with. Someone, we imagine Zaks, has tortured another person to death down here. A rather strange use of someone's grave.
And there's that automatic trapdoor "trap" being the operative expressive. Except the trap doesn't seem to work it springs open to block Dizzy's progress instead of Dizzy's return with is what you'd expect it might do and thus uses memory and makes you wonder why the room wasn't designed differently.
There's not even need to try the magnet here, even if it could attract the trapdoor back to its original position, where would you stand to position it?
Maybe it might be worth checking the pick on the pile rubble blocking Dizzy's path here, although it looks rather big to give way to that. If that actually worked at least the magnet could be checked.