Introduction to the "December 9th" Memorial Pavilion: Yingyinggou is the place where the Peiping Student Federation and the Democratic Pioneer Corps jointly held activities during the "December 9th" movement. There is a monument to "Defend North China". The memorial pavilion was built in On the eve of the 50th anniversary of the "December 9th" movement in 1984, it consisted of three triangular pavilions.