Zelda: Outlands is a game made from hacking the original Legend of Zelda ROM. It is a very thorough hack, however. The graphics have been tweaked, entire overworld has been remade, all the dungeons are new -- and just like the original game, there is a second quest, and everything there is new, too. The challenge level has also been increased over the original game. I guess one might wonder how legitimate such a game is, but if Shakespeare was able to get away with reusing other author's plots, I don't see some games can't be made this way. Outlands is great.
The game's official site is here, along with ROMs for downloading. I also got a real game cartridge, which can be played on a real NES, at NES Reproductions. (Caveat: My cartridge had some glitchy scrolling)
As usual, I played through most of the game without mapping, or needing to. Then there was one dungeon I couldn't find. The only solution was to map the entire game and see what I missed. So, I started the entire game over again on an emulator, and made a map with screenshots. I believe this is the first game I have ever mapped that way (though I am currently doing the same thing with Dragon Warrior 2). Lucky for me, as I mapped, I found an empty spot I hadn't explored which led me to the missing dungeon.
This map is for the first quest. I may do the second quest later.