As an aside, did you manage to destroy the sentinels? If so, how?
_______________________________________________
EDIT: to answer my own question, you can't destroy the sentinels (in the original version, you could negate their immunity with the Death Knight Bane spell, but that doesn't work in EE).
However, behind one of the sentinels there's a pressure plate; step on it and that sentinel will be destroyed. You should then be able to get to the hatch leading to the plateau fairly easily. You need to be using invisibility throughout. You also need high perception, as stated earlier (mine was at 12).
Last edited by Andrathion; 26/11/15 10:09 PM.