There are a few different ways that you can get to Cave 3 in the Forest. The first way is by using the ladder near the entrance to Cave 2. Climb up this ladder and you will be able to enter into Cave 3. Another way to get to Cave 3 is by going through the hidden door in Cave 2. To find this hidden door, go to the back of Cave 2 and look for a loose rock. Push this rock aside and crawl through the opening that is revealed. This will take you into a small passage that leads directly into Cave 3.