Good God I wish they’d bring back the morrowind cave systems. Each one hand crafted, sprawling with secrets abound. I recall spelunking in that game within a single cave for multiple hours, which felt like an in game week spent searching every nook and cranny. It was amazing to finally get out of and back into the sunshine.
Oblivion caves and dungeons for the most part felt like cookie cutter nonsense, and while the Skyrim caves and dungeons felt better, the quick loop to the beginning was a persistent theme and really took away from the immersion. There were at least a handful of complex cave systems.