It's a metallic platform surrounded with glass barriers. On the outside we can see a dark metallic piece with multiple red lights.
On the opening sequence, we can see in a overview the Tylon Cybertec Corporation logo in the center of the arena, specifying that the fight takes place in the Corporation.
When Uriko enters in beast form, mettalic barriers fall for land around you where the glass barriers was previously placed. You can read on them "Emergency Measure". Then, the red light submerges the platform and the ground appearence become more earthy.