The Western Tunnels

Enter the first northern tunnel. Beware of two Gauths and a Beholder. They offer good XP but no loot.

Proceed through the next tunnel to the east. Defeat the Kuo-toan war party and search the birthing pools for Corrupted Tadpoles.

Continue east, ignoring the northern tunnel for now.

When you reach a stone bridge, cast fire resistance on a character and have them cross alone. A Flame Strike trap is halfway across, but it only triggers once.

At the door on the other side, leave most of your party outside. Buff up a single character capable of summoning (e.g., using a Wand of Monster Summoning) and enter alone.

Summon monsters at the foot of the Demogorgon statue, then retreat to your party. Five Demon Knights will appear: two near the door, two further in, and one near the statue. Fight them individually. They use Symbol spells and are worth 16000 XP each. The leader drops the Soul Reaver +4, Armor of the Hart +3, and Girdle of Frost Giant Strength. Other Demon Knights drop Two-Handed Swords +1.

Backtrack and take the northern tunnel. You'll encounter a Kuo-toan war party where the cavern opens up, and another in the passage to the northeast.

Ignore the western passage for now and go northeast. From the round chamber, take the northwestern path which leads nowhere interesting.

Enter the room to the northeast, the chamber of the Kuo-toan Prince and his two Monitors. To defeat the Prince, interact with the pools three times to drop Corrupted Tadpoles and weaken him. Loot his remains for gold, gems, Bracers of Blinding Strike, and Kuo-toa's Blood.

Backtrack again and take the western tunnel you previously ignored. A group of Drow guards a gate.

To bypass the gate: If you have 17 Charisma or Viconia in your party, you can bribe the Drow guards with 1000G or convince them of an impending attack. They will then open the gates.

Fight through Drow groups to reach the surface exit. If not skipping the Underdark, placate the Drow at the gate to gain an advantage. Use a backstab on the Drow Wizard first. You may find the Archers Eyes amulet on one of them if imported from Siege of Dragonspear. Do not pass through the gate if you wish to enter Ust Natha later.