Level 56 is about right to tackle the temple. My most recent play through had my party at level 54.

Yeah, the 'cursing' makes this dungeon somewhat difficult. You'll probably have to clear most of the enemies until after you activate the second cube. Try doing it from a distance. For some reason, archer fire isn't quite as affected by the 'curse' condition. Don't know why, though.

After you activate the second cube, run like hades to find and reach the 'bell', grab it, activate the 3rd cube and you'll get transported to the 'secret' treasure room. After that you can rest and heal in the 'treasure room' and Town Portal back to Avalon and the Lady K.

Hope this helps.