Sir Bradonnnn: A new pre-explored (ugh!) subdungeon where you can trade piety for benefits. There are three price points at 100, 50, and 20.
100: 3 compression scrolls, 1 health potion, 1 mana potion. Hilariously overcosted.
50: Dwarven gauntlets
20: Gold (not sure how much)
The middle reward might be worth the piety or the loss of exploration, but not both. The others are pretty bad trades.
The dwarven gauntlets would only be worth piety if you can pick them up very early. Finding your subdungeon early and having 50 piety free to spend is just not going to be a common occurrence. However, I think that's more a problem with dwarven gauntlets being an item you want to buy ASAP. At its price, the HP gain really needs to be retroactive.
The gold benefit depends entirely on how much, but unless Tikki Tooki is on the field that's a niche we have all too little of.
As for the 100 piety trade, it's very niche, but I wouldn't write it off. Three compression scrolls is going to result in a massive increase in inventory flexibility, essentially duplicating the tinker's core class feature. While it's going to be a rare day that you have 100 piety sitting around plus enough gold to make good use of three compression scrolls, if it does come up this is a pretty market boost to your character's power. Probably lower the cost and knock down the trade a little.
Mass09 Banking: A shrouded (yay!) dungeon that gives you a small, reusable item that consumes one gold and randomly repositions all monsters on the map. Neat. You can locker it, and with a prep cost of 2, it might even be worth taking on almost-purist runs to smooth out bad luck.
This could be extraordinarily powerful, allowing you to conserve exploration space by gambling on bringing a suitable monster into sight rather than fishing around for one. Not something I'd use until roughly half the map is revealed, but for conserving exploration space after that point this could be invaluable.
The Paan Labyrinth: A very large, preshrouded dungeon with 3 lifestealing imps hiding in it. Potentially very powerful if you know how to manipulate lifesteal or you just need mana. The imps are placed randomly.
Very cool one. If you use it for LEMMISI or BLUDTUPOWA fodder this one will be beautiful.
What is sir thawn's dungeon. I don't remember it.
5x5 subdungeon containing a grave. After you step on it, Sir Thrawn (a vampire) spawns to fight you and the room is reshrouded.