I am guessing you mean you have seen a house that is more beautiful and spacious then you expected. In which can you can say something such as "it's surprisingly spacious and beautiful" - the use of the word surprisingly (surprise), that you must not have thought it was as big and beautiful before seeing it/seeing inside.

I'm not sure if this is what you're looking for, but estate agents often use the word 'deceptively spacious' when marketing properties.

I'm new in English too. but, you may use word like lowbrow or bored house.