Simply use a skull hammer jump attack to hit the wooden pegs through their respective adjacent walls. This avoids having to navigate your way through the sewers in order to get past the gates.
Use a sidle to clip part-way through the bars and then finish clipping by rolling. This is particularly useful if you are skipping the skull hammer in a Low%, and is the only part of the Cabana Sewers that otherwise requires the skull hammer. In any other case, it should not be used as the above method is faster.