With Elden Ring, I had a similar feeling of awe when I first discovered the elevator that took me into the Siofra River, and coming across what I think was Nokron, but not being able to get in. Again, I felt a true sense of exploration and discovery because an underground city was not on my bingo card, lol.
I feel like I can name a number of fantasy games that might scratch the same itch, but I was wondering if there were any scifi games that might do the same.
EDIT: I forgot to mention that I want open world games! Sorry for leaving out that bit of information. Not really looking for games with a strong central storyline, or hub-and-spoke type games (e.g. God of War, Expedition 33, Mass Effect).