Sentinels are one of many defense mechanisms in the Amgarrak Thaig. They become hostile if they sense intruders wandering too close.
Sentinels are golems created by the smiths of Amgarrak, under the supervision of an unnamed dwarven noble and a Tevinter mage known as Nereda. They were de-activated and sealed within the thaig after it had to be evacuated due to an experiment that had gone horribly awry.
They are scattered throughout the Amgarrak Thaig, guarding rune anvils and various chests spread out amongst the different levels of the Fade. They often appear in large groups, accompanying other types of golems.
Several upgraded Enraged Sentinels are found guarding a treasure storage room in Amgarrak.
Sentinels are steel golems, and are extremely powerful. It is recommended to take on sentinels using the Warden-Commander personally, as they are usually the most powerful member in the team. It is a good idea to concentrate all fire at a single golem at once and take them down one at a time.
In the room with the green fade switch, there are 4 enraged sentinels and 2 enraged watchers; the watchers are elite enemies, and all the sentinels are boss rank. This battle is extremely difficult. Be sure you have all your party assembled and pick up Group Heal for the Runic Golem before you attempt it.
One strategy that has been successful is to leave most of your party in the Sunken Grotto, while sending just one character to activate the golems (ideally someone who can resist being stunned or knocked down). That character will lead them down the hallway, and you can set the party loose as soon as they get to the door that opens into the Sunken Grotto. The goal is to trap them in the hall so that you can work on one or two at a time without getting clobbered by the others.