Here is a Metroid hack which hacks the whole map layout to explore!
Made in the Summer of '00 with MetEdit. I have done the biggest best map I could with that very limited editor.
Map + mini-walkthrough: https://goo.gl/photos/RckYowjz5VjWW8oi7
Metroid (USA).nes - NOINTRO
CRC32: A2C89CB9
MD5: D77C8053168DA14B360BF5CAECCC5964
SHA-1: ECF39EC5A33E6A6F832F03E8FFC61C5D53F4F90B
SHA-256: E6E6B7014685ADAE447EBB3833242815747BC1E5DF83ADE79F693FB67CF565B6