I never thought I'd see someone do 100% bananas guides. I've beat this game at least 5-6 times throughout the 19 years of playing DK64 and now I can go to this when I'm struggling with Diddy's bananas. Thank you, sir.
Weirdly the last balloon I needed was in the room at 4:06. I already had the golden banana but the doors never opened. I went back down and redid the button and still nothing, but when I hit 1 to try again is when they came out. 🤷🏼♀️
The level is designed so that you use the warp pads to move up and down the castle. You almost never have a reason to walk down the path since you can just get everything on your way up and teleport back down. That last balloon is so out of sight though. You'd never see it unless you randomly decided to walk back down or if you flew around endlessly with Diddy's jetpack. Not to mention the bridge itself curves outwards from the castle as if it was intended to divert your eyes away from the balloon on your way up.