Gladiator School

Model of a school for gladiators discovered using ground-penetrating radar at Carnuntum in modern Austria:

Thick walls surround 11,000 square meters (13,160 sq. yards) of the site, and the school and its adjacent buildings stretch over 2,800 square meters ((3,350 square yards).

Inside, a courtyard was ringed by living quarters and other buildings and contained a round, 19-square meter (23-square yard) training area — a small stadium overlooked by wooden seats and the terrace of the chief trainer.

The complex also contained about 40 tiny sleeping cells for the gladiators; a large bathing area; a training hall with heated floors and assorted administrative buildings. Outside the walls, radar scans show what archeologists believe was a cemetery for those killed during training

I couldn't find any GPR pictures of the ruins, but I did find this picture of a statue of Jupiter Dolichenus unearthed at Carnuntum.