Why isn't the city in Thorn Valley underground?

This really irritated me. In the first movie in order to hide they had to live underground. In this movie they live topside and it is so noticeable. Mr. Ages tells Timmy they have to live in secret but the town is so freaking noticeable. I would understand if like the NAME suggested Thorn Valley was full of thorns and not a commonly visited place but it's not they even live near humans. The humans can't live to far because they can walk to there in one day.