There are many supposed paths to immortality, though few have been tested, and those that have been tried have just as often proved to be mere flights of fancy, fashionable cure-alls with no real effect besides the status they grant those able to acquire them. Another means of achieving immortality is said to exist, but it has only been attempted by the most volatile and unstable. It's also forbidden, both by governments across Tamriel and by the Mages Guild. It's said to involve the binding of a Daedra through blood sacrifice.