That's a somewhat sad question, because we hardly know. Not enough written record exists and "paganism" was increasingly outlawed during the past millenia to the point where we're out of people that had it handed down to them. The missionaries doing most of the recording were also the ones actively suppressing its survival. I'm aware of at least one revival movement that was active during the last 50 years, but the main instigator seems to have died without leaving a meaningful succession, and thus the preservation may very well have failed. Unless someone invents a time-machine a la Assassin Creed.