The stadium.
It was the regular venue for large-sized events.
On that day, a giant cutout poster stood at the entrance of the stadium. It was a cutout of Yun Rou. Another larger-than-life poster of her face adorned on the sidewall of the stadium. It was an announcement on Yun Rou's world tour. It described her as a national hero and the most talented pianist.
By right, Xu Weilai should have known this. But, the ill-feeling in her heart blocked her from noticing anything related to Yun Rou during this time. She didn't even realize that it was Yun Rou's first concert on that day.
The day before, on the terrace, Yun Rou had invited Gu Yu to watch her perform, hadn't she? It was why she had said "see you" to Gu Yu. She was referring to the concert.
It appears that Gu Yu had agreed to Yun Rou's request; it wasn't for some business matter, after all. He had decided to watch her perform and support the first concert of her tour. Was it all about this?