Break on through Achievement
Break on through50
Pass through 4 rocks with the red anchor
A couple of levels into Waspfish, you will be introduced to the red anchor. This allows you to travel through solid objects for 10 units of movement. This is a cumulative achievement, meaning you do not have to travel through four consecutive walls in one go. That means this will come with natural progression of the levels, or you can just skewer through the first four walls you see if you desire.