There's no map in this place. Go down the stairs and straight up. Continue until you reach a hole. When you're ready, fall down it to battle Ganon.
Simply hit him with your sword while avoiding both his trident and the fiery bats he creates with it.
Eventually he exclaims that you are powerful and blows the torches out. Use the Fire Rod to re-light them. Hit him again when he stops moving and he'll turn blue, so stick a Silver Arrow in him. After doing this three times he'll finally be defeated. Once back outside go through the teleporter and down to the centre area where Zelda (and the Mole, if you talked to him) are waiting. Wait with them until the week has past to see the good ending.
If you talked to the Mole, he dug up the greatest cache of all–1400 rupees! Go over to the cliff to talk to Zelda then just Turbo-key and enjoy the ending!
You solemnly put the Master Sword in its pedestal to rest once more, and... you vanish! You have gone back to the world from whence you came. You saved all of Hyrule, and they did not even know your name. Sasharhala walks off. Zelda takes one last look back, and then she too departs.