The first Castlevania game on the NES is a classic and one of my favorite games ever.
Here you will find the numerous hidden areas, meat locations and secret things scattered throughout the game. This is absolutely incomplete and I believe the locations change during the second playthrough. Perhaps you'll find this useful.
Note the first images sets up the second images below. I.e. the first shot shows you where to crouch and the second shows you where the item pops up.