Translation:The stadium is very big.
I said "stadiums are very big" and it was marked wrong. Without あの, その or この, how are we meant to get the correct context
I hope now 'Stadiums are very big' is accepted. Japanese is very ambiguous about articles. Like skipping 'I', it depends on what you are talking about. If you are already talking about this particular stadium and say かいじょうは大きいです。then it means 'the' stadium.
会場 means = 1. assembly hall; meeting place; venue; grounds, but not stadium. Here venue fit well.
There is no differentiator in the Japanese for number of places or venues , as you would expect, so multiples or singles should be accommodated in the valid answers.
what about arena? I keep wanting to say arena. And get it marked wrong :/
To give this sentence a little more colloquialness, you could say 「かいじょうがでっかい／ or でっか"」, meaning huge and I hear it a lot with native speakers
That is the slang version.