Lalbagh Fort
The most important Mughal relic is the Lalbagh Fort. This was perhaps not so much a military fort as a secure garden complex where the Mughal governor, or nawab, could attend to business or leisure. Bengal was the wealthiest province of the Mughal Empire, and its governor was usually someone important. Construction was begun in 1678 by Prince Mohammed Azam, son of Emperor Alamgir (aka Aurangzeb), who was Nawab at the time, then continued by his successor Shaista Khan, Alamgir’s highest ranking nobleman. According to popular legend, when Khan’s daughter, Iran-Dukht, suddenly died in 1684, he suspended work on the Fort, and built her tomb within its walls. Iran-Dukht, who had been betrothed to Prince Azam, was also known as Pari Bibi ("Fairy Lady"), and her tomb bears this name today. When D’Oyly sketched the ruins of the fort around 1814, the Buriganga River still flew past its southern ramparts. What you see here is the southwest corner of the fort. I am not sure what these massive pillars supported.
Here is a view of the south face (river front) of the main gate in the 1870s. This gate is located in the southeast corner of the fort. Today we normally only see the rear of the main gate, as the area outside the fort is filled with buildings, such as the area from which this photo is taken. Note the chhattris and guldastas on the south face, which do not survive today:
This last pic (I believe) is one of the Fritz Kapp series from 1904. Note that the chhattris and guldastas no longer exist. This may simply reflect the passage of time, but Dhaka was also badly damaged by a tornado in 1888, so that may have been the cause of the damage.
Today Lalbagh Fort is one of the rare stories of successful conservation in Old Dhaka. The surviving structures within the fort include an audience hall / hammam (bathhouse) complex, the tomb of Pari Bibi, and a mosque. The mosque actually predates the fort itself, being built during the reign of Shah Jehan, but the original domes were damaged and were replaced by the fluted variety more popular under Alamgir. Since there are many beautiful exterior shots in the Dhaka Landmarks thread, I will only repost a few here (from Tmac's postings) for reference. Clockwise from top left - interior of the main gate; Pari Bibi's tomb with the domes of the mosque peeking out from behind it; rear view of the audience hall / hammam; and a section of the battlements.
However, I have not seen pics of the interiors of these buildings posted elsewhere in Skyscrapercity, so I will post some here. The audience hall / hammam is a two storied structure with the hall on the upper floor and the hammam (bathhouse) on the lower floor. In Mughal times, hammams were not only for bathing but were also a place where meetings could be held in a climate controlled environment (hot water would provide warmth in winter, and vice versa). A couple of pictures of the interior of the hammam:
Below left, pic of the roof of the upper storey audience hall. This is a chau-chala style roof (modeled after the roofs of village huts in Bengal), a homegrown archtiectural motif later adopted and used extensively by the Mughals. Below right, a pic from early in Alamgir's reign showing Muhammad Azam as a child, at the foot of the throne on which his father is sitting. Standing behind him (purple tunic) is Shaista Khan.
Finally, here are some pictures of the interior of Pari Bibi’s tomb. The first picture is of the cenotaph and the last is of the interior of the dome. Note the use of marble and stone, rare in Bengal as neither are available locally: