There are 4 levels each with 10 switches, one opens the door, the other a chest containing a weapon for each of your party member.
Since you officially already ended the game (you got the achievement) and there is nothing further to do after the mine they are bit useless, you don't even get another bossfight.
However right or wrong switch you will fall and have to start all the way from the beginning again each and every time, and with so many enemies it gets tedious.

Counting the switches from left to right: 1,2,3,4,5,6,7,8,9,10.

The correct order (from floor 1 to 4) for the doors are: 5,6,9,6
The correct order (from floor 1 to 4) for the chests are: 8,2,6,4

So that makes:
Floor 1, switch 5,8
Floor 2, switch 6,2
Floor 3, switch 9,6
Floor 4, switch 6,4