BG3 Underdark or Mountain Pass? You can explore both

You do not have to permanently choose one route at the first fork. A practical order is to settle the Grove conflict, explore the Underdark, then visit the Mountain Pass before advancing deeper into Act 2. The important part is the warning: entering a new area can advance unfinished quests.

Before crossing a warning

Resolve the Emerald Grove and goblin conflict in the way you intend, and check related rescue quests in your journal. Entering the Mountain Pass or Shadow-Cursed Lands can resolve some outstanding Act 1 events. Make a manual save before accepting the transition if your mode permits it; Honour Mode has a single-save restriction.

Choose where to go first

For the Defiled Temple entrance, pass through Priestess Gut’s quarters to the room with four rotating moon discs. Turn them until the four black new moons sit on the illuminated southern disc; enter the opened passage and climb down to the Selûnite Outpost. A hidden locked lever can also open the way if discovered and picked.

One Underdark entrance is beneath the Goblin Camp through the Defiled Temple; exploration leads to dangerous encounters and supplies or rewards. The Mountain Pass leads toward Rosymorn Monastery and the githyanki crèche, relevant to Lae’zel. Rest, bring healing supplies and check party resources before either route.

You can return and explore the other route, but that is not a promise that every quest stays unchanged. Read each transition prompt and complete time-sensitive objectives before advancing. Later Act 2 has another major point of no return; do not treat entering the Shadow-Cursed Lands as the only irreversible boundary.

BG3 Wiki: time-sensitive activities · BG3 Wiki: Halsin’s routes · BG3 Wiki: Defiled Temple