Aha! Double-jump GET! That opened up huge amounts of map for me to get to, although lots of items are still out of reach. I suspect a flying or super-jumping ability to become available at some point.
I’m really loving this, although I think I’ve found the entrance to Dracula’s room already. I can’t get there yet (there’s a jump I can’t make), but I’m running out of places to go. I did find out that my save file data shows how much of the castle you’ve explored – I’m at around 50% so far. That can’t be right, surely?