I think I see what you mean by tunnels. :)
More ideas for obstacles or arena decorations?
Viewing post in Obsticals
Hmmmm...
Energy Pendulums.
Wall Mounted Laser Turrets.Landmines.
Elevators.
Floating Platforms.
Dark Stages, maybe?
Sprint Pads (They make you run super fast in one direction)
Wall Spikes (Combine those with Sprint Pads)
A malfunctioning robotic dog head barking lightning from the walls.
The Emperor's shiny neon ba- *gets stabbed by an energy sword* AHHHH!
PS Last one should not be taken seriously, please