Turbo Tunnel is the third stage from Battletoads. The stage apparently takes place on the insides of a gigantic creature. Though it is probably the most infamous stage in the series due to the sudden spike in difficulty, it is merely a taste of what's to come.
The first section of the stage is a simple beat 'em up area where you beat on some Giblets and jump across small chasms. Halfway through you'll have the first encounter with the 'Vaders.
You'll eventually hop onto the Speeder Bike, which is where the real action starts. The first course introduces you to the most common barriers, with a simple alternating zigzag pattern. The second course introduces the ramps, which you must hit to jump across the larger chasms, as well as a floating barrier which will hit you in case you jump. Third course speeds up the action, adding floating ramps and Rat Rockets which will drop barriers in front of you.
The fourth course gets even faster, adding only the Rat Pods which you must carefully dodge as well as chasms you must jump without the aid of the ramps. The final course is the toughest of them all, with alternating zigzag barriers which don't blink like the the previous ones and come lightning fast. There is a warp near the bottom of the screen in this section, after the 9th barrier, which will take you straight to the 5th level, Surf City.