Metal Spider Temple
Here is a list of the curses inflicted as you explore. I wasn't exploring one tile at a time, so there is some error
~15 Tiles: Poison
~24 Tiles: Mana Burn
~39 Tiles: Corrosion
~44 Tiles: Corrosion
~49 Tiles: Corrosion
~55 Tiles: Weakening + Corrosion
~59 Tiles: Weakening + Corrosion
~64 Tiles: Weakening + Corrosion
~69 Tiles: Weakening + Corrosion + Warning of impending doom
~72 Tiles: Death
It is just barely possible to get the Fortitude Potion, Burn Salve, and Whupaz, allowing you to get the Whupaz with no permanent damage. If you can use the ENDISWAL glyph, then you can also get the healing potion. If you worship Jehora Jeheyu, then venturing into the spider temple just prior to purchasing chaos avatar is another way to get out unharmed.
LEMMISI and BLUDTUPOWA attract The Spider's attention just like normal exploration.
With foreknowledge and careful planning, this is potentially one of the best subdungeons to find. A possible scheme would be:
1) Wait until you need to heal AND there is a visible monster you want to fight.
2) Enter the Temple and take 4 steps south (eg 12 tiles). This will fully heal most characters. Leave and finish your business with that monster topside.
3) The next time you are out of health and mana, AND you can easily level up off of popcorn, return to the Temple and head south again until you are level with the Fortitude/Burn Potions. This will trigger both the poison and mana burn effects. Leave and level up.
4) Immediately return to the Temple and touch the altar. You will drain all of your health and mana but receive a very strong Essence Potion.
5) Go ahead and claim the Fortitude Potion, Burn Salve, and Whupaz. The exploration will refill your health and mana, at the cost of some easily cured corrosion and weakening. Characters that can stand operating under some corrosion and/or weakening may wish to parcel this exploration out over several trips. This is a very good option for Bloodmages.