Plain, I think I have had it for over 20 years
I wouldn’t bother trying to resurface enameled cast iron, but regular cast iron is easy. Sand off all of the flaked/blistered stuff, right down to bare metal, getting it as smooth as you want (smoother is better, IMO). A palm sander works fine. Inspect it VERY CAREFULLY for cracks. If you see any cracking, even the tiniest, toss it. Then reseason it by your favorite method. The Lodge website has plenty of information on this.
I’ve had my cast iron skillet for almost 50 years, though I no longer use it every day. My mother had a 70-year skillet, but I don’t know where it went after she died.