In Tera you had actual full open world labyrinthine dungeons. It was lovely to mount up from the village or town or w/e, horse across some lavish countryside, and ride right into a dungeon. No loading screens. Of course this was a lot more significant in Tera due to openworld pvp, but still, it was enjoyable from a pve point of view too. You could meet people in the dungeons, and party up for ( shock! ) hard to beat boss monsters in the open world. Tera is pretty old now, but it's open world is pretty amazing.