Doesn't even have to be big.

Years back I was touring a local datacenter that was more than a bit quirky, but their offer was basically that they had fiber loops into the main carrier hotel a few blocks away. This was useful because the guy than ran the carrier hotel wouldn't even return your email unless you were from BigCo.

But anyhow, walking around he pointed out one cage and said something like "And that's the NSA's cage, we don't ask what they do haw haw." At the time I mostly thought he was just exaggerating or joking around. But later after revelations of the scale of bulk collection I had to wonder if it really was true and simply banally that much in the open.