Originally Posted by Raze

The hallway in Maxos temple (opposite the chamber with the bedrooms upstairs) you can use to access that teleporter had been blocked by a visible force field until you defeated Amdusias.

BTW, your first encounter on Sentinel Island you can mindread to go up a level, so the higher level you are (in D2:ED I made it to level 18 in the fjords) the more of an experience bonus that will be. You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus.

Welcome to the forum. wave

also, save all your mindreading just before you go to the island. When you go there, mindread the person that first talks to you and it erases any debt and levels you