How about a long flowing downhill (via tube) to the Ocean bottom? You can make a nice spiral climb back uphill (think Tornado Vortex). Make it really dark at the bottom and have really cool sea life like Anglers and Giant Squids as you progress back up the climb. The Ocean gets brighter as you ascend from the depths with varying sea life as you climb. Can begin or end right at the Pier by the Ferris Wheel.
Creating worlds to bike thru takes a lot of graphics. I think this could be much simpler to render and would add another vertical option of a completely different nature.