Examples: Castle Daventry, Mannanan's house, Connor's house etc.
The house I would own would be Mannanan's. Its small and has secret passages and a library. If I could have all of the Green Isles with it, I would pick the Castle of the Crown in the Green Isles, but if I'm only getting the house then Mannanan's would be neat.
But it would have to still be on the mountain.