well this has nothing to do with the actual underworld i don't know if at all it exists.
this is about a fish that i recently came to know about , and i am not talking about any ordinary fish
i am talking about the lungfish also known as the salamander fish these are freshwater fishes but the best thing it can do is survive on land without water in its captivity for not only days but months,where some have two lungs where as some only have only one.
so what makes it so special that it has a very highly evolved respiratory system which enables it to breath like other creatures that live on land where it can take the oxygen straight from the air without the help of its gill
ever heard the possibility of a fish drowning well this one can if held underwater for a long time
in this state of hibernation the fish doesn't consume food or produce waste,it relinquishes its normal needs and can sustain its survival on very low energy
i would also like to thank my friend 
and i also hope scientists could induce something similar on an cellular level which could be a result in keeping the brain active for a longer amount of time helping the ones who are dying,buying doctors more time
speaking of time it can also be helpful in making long distance travel actually possible
thank you !!