It is possible to use firewalk to get inside the terrain at the small cave seen in image 1:
Image 1: Secret cave with a chest up behind the tree
Steps to reproduce:
Step 1. Open the chest and jump up on it. this can only be done on one of the corners of the chest.
Step 2. Aim firewalk at roughly this location, the terrain will cause the targeting area to shift inside the terrain.
Step 3. You are now inside the terrain, this location is safe from all attacks since the enemies does not even try to attack you. This also seems to break the animations for the enemies trying to reach the player hiding inside the terrain.