AQUATIC RUIN ZONE
Aquatic Ruin Zone is, as the name suggests, mostly under water. There are plenty of ancient obstacles around; falling pillars, collapsing platforms and arrows launching whenever you walk past them.
This zone contains some of the irritating enemies as they tend to appear from no where. Indeed the grounders break out of walls when you least expect them right when your rocketing around a full loop blazingly fast.
Robotnik uses the aforementioned arrows against you when he shows up. Two tall ancient pillars emerge from the ground each containing four arrow launchers. Robotnik hovers above them in his pod with a giant mallet attached to the front. When he bangs one of these pillars an arrow is launched. Jump on the arrows to get the hits in.