TW: Mentions torture, abuse, death
There is not a single Order 66 scene in all of Star Wars that doesn't fill me with immense sadness (and the background music only makes it sadder). What the Jedi went through during the Clone Wars was already bad enough, but what the survivors went through after the war was considerably worse.
None of the Jedi who died on the battlefield during Order 66 knew what they were being executed for. A lot of them never even had a chance to fight back, and their deaths were brutal.
Operation Knightfall was the name of the attack on the Jedi Temple. The Jedi who were in the temple tried so hard to protect the children and most of them died doing so. Anakin Skywalker murdered countless younglings, and it is so sad to think about the fact that, for one brief moment, those children believed he was coming to save them. They died in terror at the hands of someone they looked up to, admired, and trusted.
The number of lives lost on that day alone is devastating, but for many Jedi Purge survivors, what came after was a fate worse than death. For them, life became a walking nightmare.
Fortress Inquisitorius is the deepest circle of hell. What Jedi survivors went through there was pure torture.
This is why so many Jedi were on the run, in hiding, and cutting themselves off from the Force. We watched Yoda, Obi-Wan, Ahsoka, Kanan and Cal survive Order 66 and they immediately found themselves alone in a galaxy that criminalized their existence. It became a criminal act to provide aid to surviving Jedi or other Force users too.
Those kept at Fortress Inquisitorius never stood a chance though. Cere Junda escaped the first time after being relentlessly tortured and forced to watch her padawan give in to the dark side by becoming Second Sister. She channeled the dark side and killed everyone (except for Trilla) and ultimately escaped a changed person. She cut herself off from the Force entirely because her experience had traumatized her so badly. When faced with having to return to Fortress Inquisitorius, it was clear she was scared and that she wasn't okay. She was having to face her past and the part she played in Trilla's fall to the dark side. She had to watch in horror as Vader executed Trilla for failing her mission. In her rage, Cere tried to use the Force to completely crush Darth Vader until Cal stopped her.
Fortress Inquisitorius is such a dark and desolate place, located largely underwater. There is no sense of day or night, no real concept of time. There was no light at the end of the tunnel, no sense of the outside world. There was nothing but pain and death. To the prisoners there, it would have felt like an eternity of endless suffering. The light they once held so dear was no longer in their grasp, replaced by the sheer terror of darkness as the Empire abused them in every way they could.
Operation Knightfall, lead by Anakin Skywalker, couldn't be a more appropriate name. Jedi Knight Anakin Skywalker fell to the dark side. Many Jedi fell in battle and in the temple. Survivors who were captured were tortured into falling to the dark side. Night fell on the galaxy as the dark side of the Force gained the upper hand by eliminating those who served the light side.