The correct answer is D. Dharokha-Darpan.
The Platform of Bhopal Singh is a large platform located in the center of the fort. It is made of red sandstone and is decorated with intricate carvings. The Sheesh Mahal is a palace located in the north-west corner of the fort. It is made of white marble and is decorated with mirrors. The Diwan-e-Khas is a hall located in the south-east corner of the fort. It is made of red sandstone and is decorated with intricate carvings. The Dharokha-Darpan is a window located in the south-west corner of the fort. It is made of white marble and is decorated with mirrors.
The Platform of Bhopal Singh is a popular tourist attraction. It is a great place to take in the views of the fort and the surrounding area. The Sheesh Mahal is also a popular tourist attraction. It is a beautiful palace that is well worth a visit. The Diwan-e-Khas is a less popular tourist attraction, but it is still worth a visit if you are interested in the history of the fort. The Dharokha-Darpan is the least popular tourist attraction in the fort. It is a small window that does not offer much in the way of views or history.