Noah’s ark does exist but this is simply the name of the project that we created in order to save all animals from the huge tsunami waves caused by an intergalactic attack on the planet. That was the day when we created the ark that was able to hold several thousand species in order to preserve them. We also hid many of them underground just in case something awful occurred to the ark but everything went smoothly.
The ark is currently docked underwater in a special laboratory in the Pacific Ocean. We have plenty of hidden labs underwater and we also hold some creatures that are thought to be extinct. Such as the case with the Carcharodon Megadolon and a few dinosaurs that we also keep hidden for security reasons. A few Megalodon sharks would probably destroy all large vessels and cause serious damage. The same goes for the creatures we have hidden that could roam the lands and destroy cities if released in modern times.