My tip“Entry is by a token donation, and the visit takes half an hour; it looks best from the opposite bank (Triana) at sunset.”
A polygonal defensive tower built by the Almohad governor Abu al-Ala Idris around 1220 CE on the bank of the Guadalquivir. A chain ran from it to a tower opposite to close the river to ships. Today it houses a small maritime museum.
Address
Paseo de Cristóbal Colón s/n