I've got the Compass of Light now - it took two attempts since I couldn't work out how to defeat the three flamethrowing warrior-type enemies, until I fluked on the fact that I could use my whip to grab their shields and then hit them. I was trying to get Zelda to go around the back to attack, but that was easier said than done.
I'm now on my way to the dark realm, but there are two stamps missing in my passport. I reckon I've missed stamps in the Dune Sanctuary and possibly in Goron Village, but for the latter I've no idea how I missed it - plus the Valley Sanctuary stamp might cover that. We shall see.