The tower of eternity is located in the forest of jigramunt(near the warp room area). Once you get in it theres no turning back. You have to pass 50 floors each with a different kind of enemy(you get a potion after passing 5 floors). After you passed all the floors and reach the terrace, you'll find an item called ''kit bag''. Now jump out from the terrace and you will come back to the ground unharmed.