DALLAS -- Here at WFAA we try to get to the bottom of your questions. A viewer emailed us saying, "I heard that there is a giant underground tank under Cole Park in Uptown Dallas...is this true?" Our VERIFY fact checkers went searching for the answer.

Short answer, "yes," there is a giant water tank under Cole Park in Uptown, but giant may be an understatement.

"Once we turn the lights off, you can't see the hand in front of your face," Dhruv Pandya with Flood Control Operations For the City of Dallas explained.

Panya took us deep underground for a look at the Cole Park Detention Vault --120 feet deep below the surface.

It's truly something to see, 13 chambers can hold up to 50 million gallons of water. A solution devised by the city after a series of catastrophic flooding events in the early 90s.

"This gives us the ability to bring the water in here, hold it until the rain event is over, and then we can push all the water out," Pandya said.

During severe weather events, water from Mill Creek begins to fill up these massive 840-feet long, 24-feet wide tunnels dug into limestone.

"See that line, that's how high the water has gone before," Pandya pointed out.

That water line is about 60 feet from the bottom of the tunnel, proof that the system is working.

"This is an engineering achievement, and it's been functioning since it came online in 1993, and it's been doing its job."

Doing a job so well that most people at the park likely have no idea what's happening right under their feet.