There is a rumor of a hidden enemy named "Test 0" which could only be fought at that area. If you believe everything you read, it is supposed to have tons of HP, but is not a threat as it does nothing all battle, so the only problem is it takes a lot of time to kill, but if you do you suposedly get masses of EXP and AP.

There is a chance that Test 0 was a "Monster in a Box" type battle, even though I don't think FFVII had any battles like this, but it would fit in perfectly if it was true.