Not many realize that this is a shot not of before the water was pumped out, but after it was put back in. After they found the Door, at the very bottom.

Thankfully one of the sandhogs was a grizzled, salty type, still familiar with the Old Stories. The giant bronze Seal was covered in ancient muck, and heavily oxidized. They almost broke it. But the old vet washed off some of the mud and slime, and instantly knew what it was.

Those tunnels are sealed off, now. Most of the plans showing their location destroyed. But the pool is still down there, and the Door, and the Seal. And what lies beneath that, in the deep forgotten dark.

It waits. And it seethes.