Fortress Inquisitorius was a heavily armed underwater stronghold located on the moon Nur. It served as a headquarters of the Imperial Inquisitor Program after they were moved off their previous headquarters on Coruscant due to the rogue Inquisitor chase. The existence of the fortress was hidden from the majority of the Empire to maintain the public perception of peace and security. In reality, it was where the Empire took the Jedi they captured and turned them to the dark side by brutal torture turning them into Inquisitors. However, the Imperials were unable to corrupt all of them. The fortress was known for its torture. In 14 BBY, during the Great Jedi Purge, a mission took place at the fortress and Trilla Suduri was redeemed and killed by Darth Vader.
One of the new pieces of concept art for the Obi-Wan Kenobi series shows us some sort of Imperial base. To me it appears to be underwater with that green glow and what I think are fish outside of the windows. So where is this? My current theory is that it could be the Fortress Inquisitorius on the planet Nur. Located near Mustafar it was where the Imperial Inquisitors were stationed when they weren’t on Coruscant or off hunting Jedi. We first saw the fortress in the game Star Wars Jedi: Fallen Order, and much of it is underwater. With mention of Jedi hunters playing a role in the series, I think it’s very possible we could be seeing it in live action.