Walk down to the lower left area, use Gollum to climb up and hit the boulder to make it drop down. Use Sam to jump up and dig up a skull, then throw it at the plants to the right. Use the rope to pull down the plants. Switch to Frodo, go back to Sam's location, jump across the vines and to the other side. Light up the cave, hit the object behind, build the slider and push down the rock to the lower area. Build the stairs, then light up the cave below. While Frodo is still inside the cave, switch to Sam, enter the cave, dig up and build a turnstile. Use the turnstile, use Sam's rope and pull down the pillar. Build the wooden parts and burn it using Sam. Build the next set of stairs and climb up.
Go to the upper right area, dig up and build the slider. Use Frodo to enter the cave on the left, switch to Gollum and climb up. Push the boulder down, then go down and push the rock to the upper right area, climb up. Use Frodo on the cave at the upper right, smash things inside and pick up the rock. Throw the rock to the webs located outside to the top left. Use Sam's rope to pull down the pillar on the left. Climb up the vines and shimmy to the left. Continue upwards through the stairs. Hit the webs and have Gollum climb up. Once on top, hit more webs and build a see-saw, jump on the left side of it. Go back down and continue to the right. Use Sam to crawl under the hatch and grow some plants. Go down and build some steps, jump up and continue upwards.
Continue upwards through the cave, when you see the fork, go to the right. Hit the debris. Move along. Go to the upper right area to find a climbable wall for Gollum. Get Frodo close to the spiders to scare them away, climb up using Gollum. Push down the rock, then switch to Frodo and crawl under the hatch. Follow the path forward using Frodo, hitting the webs along the way. Destroy the skeleton and build some bars, then pull yourself up. Smash all the objects around, build a basket, then pick up the rocks and throw them at the basket.
Follow the path downwards to escape the giant spider.
Follow the stud trails to reveal the next chapter.