I'm going to get into spoilers here, so if for some reason you haven't completed or played this game yet then hurry up and get to it, you're already fucking years late.
Anyway, a ways into the game you discover that the castle is being lorded over by none other than Richter Belmont, the protagonist from Rondo of Blood. This is where the game gets interesting because from here, you can go straight to Draculas's chamber, go and ruin Richters shit and the game will end right there.
I like to call that ending, the "lazy shit" ending, because if you go to any lengths to explore the castle (which is sort of the point of the game) then you can easily find a pair of holy spectacles. With these equipped you can see this little green orb when you fight Richter, and killing the orb instead of him opens up a entirely different castle!
OK, maybe not entirely different, it's the same castle flipped upside down. This sounds awful at first since it sounds like a bunch of backtracking through the same areas and having to complete the exact same game again, but it's actually really cool. New items to find, new enemies to battle and bosses to defeat, basically new everything except backgrounds.
What I find so amazing about the reverse castle though is that the developers put it in, and made the whole thing entirely missable. There was no guarantee when this was a new game that every player would figure that out, they programmed all this shit and it would have been totally lost on some players.
Shit like this is awesome, and with Symphony's reverse castle you're essentially getting 2 games in one. So if you needed MORE of an excuse to pick this up on XBLA or something like that, now you have one.