What is the code to Nolan's Hideaway on HorseIsle?

On Horse Isle, Nolan does not live in a hideaway, so a code isn't necessary. I think you are talkng about Nilan's Jungle Trap Hideout quest (the one that asks for 100 walnuts).

To reach Nilan, you will need to go through the maze. Stand on the sign, dismount your horse, and walk:

1 up.....3 left.....2 up.....5 right.....1 down.....4 right.....5 up-.....2 left.....2 down.....2 left.....

2 up.....1 left.....2 up.....2 left.....4 down.....2 left.....6 up.....6 right.....3 up