Head left for a bit, and your old friend the Crystal Monster will show gobble up one of your party members. Don't worry - you'll get them back.
Head left and keep descending. The water you pass by is an electric eel tank that will come into play later.
Hop over the first gap as you descend to encounter the Hunter, who tosses a tape recorder your way. Pick up the recorder, but don't approach her - she shoots!
Continue your descent and head left. When you reach the Crystal Monster, approach to have him toss you to his other side, where your missing party member can be found.
Climb the ladder and hop up the platforms to find a crate. Push it down the platforms until it reaches the ground, and then push it to the left.
Use the crate to hop to the high ledge, and head left then up. You'll find a Cave Painting up here.
Now take the lower path to find a previous team that tried to survive the cave. You can pull a dead battery from the dead robot, so do so.
Return to the ledge above the crate and have a party member pull and hold the lever to raise a lift below, revealing a passage. If you haven't brought your third party member to the rest of the group yet, do so now.
Have a second teammate drop into the passage under the lift and hold the lever there, raising a gate. Your third member should then take the dead battery and exit through that gate. Also, there is a Cave Painting on the far left of this lower passage.
With battery in hand, head all the way back to that electric eel tank. Hop in, and after a few seconds the eels will emit a charge, shocking the battery back to life. Before you head back to the rest of the group, check out the Cave Painting on the left side of the tank.
Return to the group and place the charged battery into the recorder. Now run the recorder back through the passageways and drop it in front of the Crystal Monster.
Release the lever holding the lift and push the crate onto it. Pull the lever again to elevate the crate near where it came from. Push it off the right edge of the platform, and it will fall onto the Crystal Monster. The monster will scream, and that will be recorded onto the tape recorder.
Run the recorder up to the Hunter and drop it nearby. She'll hear the recorded scream and run off, giving you access to the hot dog machine.
Get a hot dog and return to the Crystal Monster. It will slowly move toward you while you hold the hot dog, so walk to the right until you cross the bridge you've passed several times now. The monster's weight will break the bridge, and your party can jump down to continue their progress.