Back in the day when 'everyone' was saying the world was running out of oil (Jimmy Carter days) some people built some VERY nice earth-bermed homes. There's 3 or 4 within about 10 miles of my office that I know of. I've gone thru 2 of them on realtor open houses; good quality, usually built into the side of a hill.
Whenever I'm presented with an offer to appraise one, I'm always too busy.
They generally sell for about the same, maybe a bit less, $/sf as conventional construction but take 2-3X longer to sell. Part of the problem selling is the buyers need an in-house lender.
About the same market appeal as a dome home; there a couple of those around here too.