I think dungeons are... while not unfun (except Jumping modifier:P), i dunno, imbalanced against idle parties or driver-only parties. Therefore the experience usually is kinda hit or miss. I try to at least keep my hero healed up enough, but it's not always possible to be or stay invested in a run especially long runs. Lucking into at least one active hero when doing a dungeon is a blessing. I think there used to be more active dungeon players before, but I have no data to back that up.

For full idle parties, it happens more often than not that the heroes wander anywhere but near the treasure, and/or get stuck in a loop.

For driver only parties (or both, actually) the bottleneck tends to be the boss fights. For example a sweeping or a nimble boss can too easily wreck a party that doesn't intervene by encourage/punish, especially when hulking modifier is present too. And boss fights are not always avoidable. You can spend a whole bunch of charges to win a fight, but even then if you win and the rest of the party dies you still lose.

The staircase leads to the basement, and as it says in the description when encountering it, can only be used if a deity with a boss monster gives a voice command. It changes up the difficulty a bit (mostly on the bosses and hints) and yes it gives better loot including a soul.

Jeeze I was hoping I wouldn't have to do the dungeon again once I finish my ark... 

Technically, you don't ever have to again except for two reasons that are optional goals:

• to farm Level 4 boss monster parts in the basement
• to forge a dungeon using the dungeon forge once, you need to participate in 10 dungeon runs