Dungeon
This is a quick rundown and the zone classification of Dungeon. Dungeons can be indoors or outdoors. The reason why this is an important designation is mainly for the use of the Wand of Imperceptibility which drops rarely from a rare spawn in The Deep (#4 on the map). This is an unlimited charge shrink item. The only limitation is that it only works in zones classified as Dungeons. This works in most indoor zones where you'd want shrink from Luclin and previous. However, in PoP, its usefulness starts to diminish. Also note in the list below that Sanctus Seru, Kael Drakkal, Katta Castellum, and some others are classified as cities, not dungeons and thus not listed. There is no other use of the Dungeon classification. If one is discovered, this will be updated.
Zones classified as Dungeons:
The Acrylia Caverns The Akheva Ruins Befallen Blackburrow Accursed Temple of CazicThule The Howling Stones Chardok The City of Mist The Crypt of Decay Crushbone The Crystal Caverns The Crypt of Dalnir The Temple of Droga The Tower of Frozen Shadow The Fungus Grove Grieg's End The Ruins of Old Guk The City of Guk Plane of Hate The Hole Kaesora Karnor's Castle Kedge Keep Kurn's Tower The Castle of Mistmoore Najena Dragon Necropolis The Mines of Nurga The Lair of the Splitpaw The Permafrost Caverns The Plane of Water The Liberated Citadel of Runnyeye The Ruins of Sebilis Siren's Grotto The Sleeper's Tomb Solusek's Eye Nagafen's Lair Ssraeshza Temple The Temple of Veeshan The Deep Icewell Keep The Estate of Unrest Veeshan's Peak Velketor's Labyrinth Vex Thal The Warrens