The emperor penguin can dive more than 500 metres and stay submerged for more than 20 minutes.
Why it is true
The emperor penguin is the bird that dives deepest and for the longest time. It can reduce its heart rate and store oxygen in its muscles. The documented record exceeds 500 metres in depth and 20 minutes underwater.
Source: National Geographic
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.