That switch triggers something right there (after you cross the grate, which the T'rang sign says not to).I think you do have to follow this path though (or ortherwise get to the inside of lower martens bluff. From there you come up inside martens bluff and find a lever (after a room with an idol/statue that spits bolts in 4 directions or after a stairway up fro LMB, depending on how you get there).
That lever opens a huge door/grate in the other area of martens bluff, which leads to the idol.
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** SPOILERS galore **You will need the trang arm found in Martens bluff. That will open a door right where oyou take the elevator shaft down to LMB (lower martens bluff). Turn right, down the hall is a shimmering wall (I think). If you interact with it it asks who you are (you are marten). Down there is where you find his words.
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