Hythloth

Hythloth is one of the 7 Anti-Virtue Dungeons. Its values are the opposite of the Spirituality and Humility virtues. The dungeon is located on Fire Island. There are four levels. Hythloth is largely an Abyss dungeon, where Demon Slayer weapons will serve you well. The first two level consist of low level monsters. On three and four, some high level baddies are combined with a mess of spell casting monsters. Put another way, it's a recipe for disaster.
Only a well-organized group, well armed and ready for anything, is able to come out of it alive given that the entire basement is sealed by magical transport through the antimagical
If you feel ready to face everything Hythloth is the confirmation that you are looking for.