Optional Dungeons always spawn in every Diablo II: Resurrected game in the same zone, but they spawn in random-generated locations that you must explore.
Usually these dungeons have 2-3 Levels down, and at the end there is a purple-glowing treasure chest that has a chance to drop unique items and even Runes.
Below is a list of Optional Dungeons. Follow the links to a YouTube video. The video descriptions have a list of Mobs, Unique Rare Elites, all white/gray/blue items that dropped in the video (with timecode to jump there); and which runes and gems dropped in that dungeon (if any).
These videos were recorded in Hell difficulty.
- The Cave (Cold Plains) — lightning/fire immune
- The Hole (Black Marsh) — cold/fire immune
- The Pit (Tamoe Highlands) — cold/lightning/fire immune
- Stony Tomb (Rocky Waste) — lightning/poison immune
- Ancient Tunnels (Lost City) — lightning/poison/physical immune || SHAEL Rune
- Arachnid Lair (Spider Forest) — fire/poison immune || HEL rune
- Swampy Pit (Flayer Jungle) — lightning/poison/fire immune || ORT rune