If you want to have a great time completing the first Zelda, try playing it with Hand Drawn Gameguides.
It's written like a kind of journal with a lot of artwork and hints that don't immediately spoil the experience but give you enough guiding to find the rest yourself.
I played it so much that I did a playthrough all on one save. I had to leave the NES plugged in overnight, which is some sort of miracle that the dog didn't yank out the cord.
I'm not typically good at games, so I will still be babbling about this accomplishment on the day I succumb to advanced dementia.
It's been a looooong time, but I remember the manual saying that they were a thing that exists, but not telling you where they are.
EDIT: Found the manual online. Turns out it doesn't even tell you that much. It does tell you how to find the first two dungeons, but you can figure that out yourself without the manual. Also, I forgot one of the dungeons was shaped like a swastika, which, I know that has different connotations in Eastern cultures and Nintendo wasn't really entirely conversant with Western cultures at this point, but hoo boy.