9-inch-thick wooden bridges, securely bolted at either side and very strong. (Hardness 6, 12 Hp per inch, and Immune to Fire)
30' Lava Pit. The Rules for lava can be found on page 304 of the DMG.
Other Points of Interest
This arena is rather warm, just being in it causes 5 subdual fire damage every round. (For Undead and Cold subtype creatures this is normal damage, rather than subdual)
The walls of the center structure reach all the way to the Arena ceiling; it's walls are normal stone, except they have Fire Resistance 5; that benefit is also extended to anyone within it's walls. (Note: This is an (Ex) effect)
The ceiling of this arena is 30' above the floor.
The Arena boundary is 30' above and 30' below the floor.
Additional Lava Rules
Lava breaks line of sight, but not line of effect.
Movement in lava is handled like movement in water, except that the penalties are doubled. As with water, these penalties are negated by freedom of movement.
