El Castillo Interior or Las Moradas (trans.:The Interior Castle or The Mansions) was written by Saint Teresa of Ávila in 1577 as a guide for spiritual development, through service and prayer. Inspired by her vision of the soul as a crystal globe in the shape of a castle containing seven mansions, which she interpreted as the journey of faith through seven stages, ending with union with God .

After being ordered to write her autobiographical La Vida de la Santa Madre Teresa de Jesús (The Life of St. Teresa of Jesus), Teresa was hesitant to begin writing again on her views of the perfection found in internal prayer.. She started writing her seminal work, Interior Castle on June 2, 1577, Trinity Sunday, and completed it on the eve of St. Andrews Day, November 29, 1577, however there was a five months long interruption in between, effectively leaving a fortnight each for first and second halves of the book . In August 1586, it was decided to print Saint Teresa's works, the Augustinian monk and poet, Fray Luis de Leon was selected as the editor, and finally in 1588 the book was published at Salamanca, Spain .

El Castillo ("the castle" in Spanish) may refer to: