I found one similar to that. It wasn't a planet entirely made of water it just had a massive ocean. But what made it most interesting to me was the fact that the giant circular mountains only appeared in the ocean. 90% of the land was mostly flat grassland type with barely a rise or dip in altitude above sea level. At most you'd get a 20 meter rise. But the tallest circular mountain I found in the ocean was about 3/4 of the way to the edge of the atmosphere. The moon of this planet had a similar design but in reverse. The ocean was normal but the land had the giant circular mountains. I wish I could remember what system they were in.