One's in the north of the area to the side of the big tower, the other is to the south and you have to swim to get to it, but both say "You need the appropriate quest to enter". Now, I'm level 22 and I'm pretty sure I've done every single quest in Tortage (inc. underhalls, white sands etc.), I have an empty quest log and no quests leading back to the Acheronian ruins and into whatever's behind those doors...
So naturally I'm curious, and I absolutely NEED to know what's behind them!

Anyone managed to enter them yet? Which quest do you need to do it?