SHEN JI YUN walked upstairs with a blindfold on. Since he was deprived of his vision, his uncle was supporting him from the side and also leading him to wherever place they should go. Since there's only one place to go by going upstairs, so it's understandable where his uncle was leading him.
It's towards the rooftop deck.
Their house's rooftop deck was not usually use. But a housekeeper that came by the house every week cleaned it weekly. It also had a glass enclosure and a retractable roof that could protect the people from extreme weather and even provide insulation against the cold. So, it wouldn't be a bad idea to have a party there.
Since today was his birthday, the surprise that they had prepared for him must be there. He already somewhat expected what it could be, so now the problem was how should he act surprise. Luo Yan definitely helped in preparing this surprise, so if his reaction was stale, it might disappoint the other.