The Potala, which means "The Buddha's Mountain" is a landmark impossible to miss. It is located on the highest point --- in fact the only high point --- in Lhasa.
Construction began on the original Potala in 764. The current one was begun in 1645.
The Red and the White Palaces are the two sections of the Potala. To complete construction of the Red Palace, the death of the then current Dalai Lama had to be concealed for 12 years, which was done via the pretense of an extended religious retreat.