Introduction to the Octagonal Watchtower:The Octagonal Watchtower is where Shah Jahan, the builder of the Taj Mahal, was imprisoned by his son in his later years. Shah Jahan was imprisoned in this castle for seven years. He could only look through the window. He loved his wife's mausoleum, but could never touch a stone or pillar of the Taj Mahal again, and died in loneliness and sorrow.