The Netherworld is the Afterlife : realm and domain of the Demodragons. It was Kavaxas's former home
It is a another spiritual plane of existance were also Souls of Humans who died reside.
Notable charchters are Master Splinter and Ho Chan ,it is also from were Rahzar and his master Undead Oroku Saki ( Shredder ) was brought back to the "World of Living" and resurected from dead by Demodragon Kavaxas.
There were also unknown number of skelleton ghosts that were unleashed ,as well as Ghost of Hattori Tatsu the ninja blind-warrior who ended up in that place after his demise in S05EP2 " The Forgotten Swordsman" upon New York City when portal to Netherworld was opened.
The Netherworld portal as closed by Ninja Turtels and all Spirits of dead including Undead Shredder and Kavaxas were sent back to that place.
It has for now made its debut in S05EP4 " End Times".
Notable inhabitants :
- Master Splinter
- Ho Chan
- Unknown number of Ghosts