That really is surprising considering it’s just an island (or a few islands? I can never remember wether Ireland/isle of man is included.) It’s weird how expensive housing can get when there’s so much empty space.
Part of the island of Ireland, Northern Ireland, is part of the UK the rest being the Republic of Ireland (which everyone not in NI refers to as just Ireland).
The Isle of Man isn't part of the UK, though it is a Crown Dependency.
Edit: Surprisingly little of the UK is actually built up areas: https://www.sheffield.ac.uk/news/nr/land-cover-atlas-uk-1.74...