Sher Mandal, Delhi where Mogul emperor Humayun accidentaly died!!

Sher Mandal (Sher Shah's Pavilion). Delhi
Located within the confines of the Purana Qila fort in Delhi, is a historical building called  Sher Mandal (Sher Shah's Pavilion). This 16th century monument is believed to have been built  on the recommendation of Babur by Farid (Sher Shah) for his son Humayun and so the name was  retained as  Sher Mandal. ‘Sher Shah’ had tried to finish the building  as part of the fort, but he died
Sher Mandal (Sher Shah's Pavilion).
when the construction was in progress. So the responsibility of completing the work fell on Mogul ruler Humayun who in turn, completed the monument. The Building was built originally as a personal observatory and library for Humayun. 

This simple, but great monument is a two-story octagonal tower made of red sandstone with steep staircase leading up to the roof. Believed to be the first observatory  of Delhi, the tower is characteristic of an octagonal chhatri  atop supported by eight pillars and decorated with white marble in typical Mogul style. Inside the monument one could see  the remnants of the decorative plaster work and traces of stone shelving where, presumably, the emperor’s books were kept.

 Mogul ruler Humayun, in a freak accident, died here in 1556 after falling down a flight of stairs. This was recorded by some members of the royal court of Humayun's son Akbar. According to Fazl, a historian  on 20 January 1556 (sources give 24 January), Humayun  was on the roof of a recently fitted library to bless his subjects. The accident took place in the evening while he had just begun to descend. No sooner had he stepped on the second step than he heard the ''azaan'', the Muslim call to prayer. Humayun, when getting ready to pray,  as he stood up, one of his legs became entangled with his robe, He tripped,  resulting his fatal fall down the stairs. He sustained serious injury on his temple and died  a few days later.  The public announcement, it is mentioned,  was made  17 days after his death and by that time ruler Akbar had already reached Delhi from Agra.
Sher Mandal (Sher Shah's Pavilion), Delhi
The structure  is a mix of  Timurid and Safavid architecture, and is  the only surviving palace structure within the fort. Earlier it was thought by some historians  that Sher Mandal was built by ruler  Sher Shah Suri in 1541 as a pleasure resort. The subject of original  builder of this structure has been a serious one among the researchers and at last it was agreed it was built by Humayun. 
Researcher Ram Nath mentions that  the architectural designs of  Sher Mandal fall under a homogeneous construction  and is consistent with Humayan's style.The near-by Qal’a-i Kuhna masjid or  the pavilion resemble any of the buildings of Sher Shah.

The building, a two-story octagonal structure (about 60 feet in height is constructed of red sandstone that gives it an impressive look.It has has two extremely steep, narrow, and irregular granite staircases and there are  eighteen steps each running along the northern and southern walls connecting the two floors. There is a single staircase joining the upper floor with the terrace. The dados of the  middle story contain a 12-pointed star.  This was specially introduced as  ruler Humayun considered  it auspicious though  it is an astronomical numeral.
The cruciform chamber in the upper story is an interesting one - a single square-shaped room at the center  opens out into four smaller rooms.  The chamber has semi-vaulted softies on the sides supporting the four arches and a vaulted ceiling.  The interiors have fine designs and decorations of glazed tiles and incised stucco.
The lower story is  is inaccessible and it is presumed that it corresponds to a temporary burial site of Humayan. The chamber that was initially open, was later closed out of respect and Humayun's corpse was moved to a newly commissioned tomb  two years after his death in this building.