Sonic Heroes stg26 is Egg Emperor arena. There is another version. An early one.

Gamecube versions has the texture(test02) in s26.txd.

Xbox version has the older collision data.

s26.cl: 613 KB
s26_wt.cl: 2.17 KB
s26_xx.cl: 2.22 KB

Final
stg26.cl: 1.81 MB
stg26_xx.cl: 320 bytes

Have yet to find level .bsp meshes or object data for it though.