Bonus dungeon?

[jrodman]

So I've finished the game. I enjoyed it.

I have the option to play on 'score attack' which doesn't really interest me, and I can reload at the game's end and grind to silly levels, but that doesn't either.

However, I see rumors on the internets that there is a bonus dungeon. How do I access this? I don't really want to start a new game and go hunting for it, nor really wander the world map aimlessly possibly for hours looking if I am not going to encounter it.

What are the requirements? Maybe a hint unhidden, and a direct stament of how to access behind some sort of spoiler tags, if those exist here.

[morbosfist]

South of the desert castle, there's a gap in the rocks. You can follow that gap to some of those walk-over rocks, which form a trail to a dungeon your characters will acknowledge as even harder than the final dungeon.

[Ansive]

Beware of the fearsome dragon.