Spelunker is a medium armor set. The 5-piece set bonus adds 400 Weapon and Spell Damage to your Undaunted abilities. When an ally uses one of your Undaunted ability synergies, you restore 1500 Stamina.
The Spelunker set is part of the base game. It drops in Spindle Clutch I and Spindle Clutch II in Glenumbra. Each set item is bound on pickup. You can acquire medium armor, weapons and jewelry of this set in the Mercenary motif style.