Yeah it's one of the toughest dungeons in the game mostly due to the Wizzrobes, more specifically the blue ones. Be sure to have a red potion and the magical sword & shield before doing it to make it a little easier.
Invest in a Blue Ring or a Magical Shield to help deal with the Wizzrobes. Also, get the Magical Sword from the old man under the grave. And if you're lost, just use a map. Level 6 is definitely one of the harder ones. But Level 7 is a lot easier