Easiest to Hardest Order (Approximate)
Giants' Mountaintop Catacombs (West Mountaintops, near Zamor Ruins)
Giant-Conquering Hero's Grave (Northeast, after progressing in the area)
Spiritcaller's Cave (Freezing Lake area)
Cave of the Forlorn (Along the river in the east)
Yelough Anix Tunnel (Consecrated Snowfield / western part)
Boss: Astel, Stars of Darkness.
Mining tunnel with miners, lords, and a tough Astel variant. Requires more preparation due to the boss.
Consecrated Snowfield Catacombs
Castle Sol (Northeast Mountaintops)
Boss: Commander Niall (with dual knights).
Large castle dungeon with tough enemies (Zamor warriors, etc.). Commander Niall is notoriously difficult for many players due to his summons and frost attacks. Often one of the hardest minor dungeons in the region.