Tran Hung Dao (1213-1300) was a general that defeated the Mongols twice in the 13th century. When the king told him to surrender, Tran Hung Dao answered him that he would prefer to die before handing his ancestor lands and temples over to the invader. Nowadays he is a cultural hero in Vietnam, and a symbol of resistance.
The Tran Hung Dao Memorial sits in a Square close to the Saigon River. It is here that you can take the fast ferry to Vung Tau. There are also some boat tours to visit the Saigon River. I did not take any tour of the river, because the river did not look very interesting to me, but you may try.